The Show Must Go On

"Can anyone here play the drums? I mean someone good!"

—Pete Townshend, upon Keith Moon's passing out mid-concert

There must be some mistake
I didn't mean to let them
Take away my soul.
Am I too old, is it too late?
Ooooh, Ma, Ooooh Pa,
Where has the feeling gone?
Ooooh, Ma, Ooooh Pa,
Will I remember the songs?
The show must go on.

—Pink Floyd, "The Show Must Go On", The Wall

Accidents happen. Sometimes, a catastrophe occurs during the production of a creative work that forces it to a halt - the writer quits, the union goes on strike, or an actor gets injured or suffers critical existence failure. In recorded works intended for later consumption, this can be remedied relatively easily - scenes can be rewritten or reshot, actors can be replaced, shooting can be put on hiatus.

However, in live entertainment, the show must go on at all costs - unlike with a movie or a TV show, a live performance has an audience of potentially tens of thousands of people, who have all paid to be there, and are rightfully expecting to get their money's worth. This forces the characters into crazy improvisations, costume changes, awkward stealth to avoid further disrupting the show and any number of desperate things to keep the show going.

Note that the full phrase is something like "the show must go on tonight" (i.e. whatever personal tragedy happens during the day, everyone must be in place and ready to perform when the curtain rises).

Compare Throw It In. See also All Part of the Show, Dead Line News, Pushed in Front of the Audience.

Examples of The Show Must Go On include:

Anime and Manga

When Takako's dress is being ripped off in Otome wa Boku ni Koishiteru, Mizuho needs to improvise the way to cover her up, and end up also kissing her.
In Macross Frontier, the stunt extra aerobatic team messes up at Sheryl Nome's concert, causing Alto to knock Sheryl off her several story high stage. Alto manages to recover and catch her, saving her from a fatal fall. Her reaction? Annoyance, and she tells him to get flying and make it look good while she continues singing, because the show must go on.
- Later in the same concert, an air raid siren sounds ushering everyone to the nearest shelter. Sheryl's reaction: "But I'm not finished singing yet!" The trope is subverted, as Cathy drags her off stage.
In one episode of Mermaid Melody Pichi Pichi Pitch, there was a play called "The Mermaid Princess", which is based on Hans Christian Andersen's The Little Mermaid, took place in the school. Despite Lucia's clumsiness, and a (real) attack from the water demons, the show continued thanks to Rina's quick wit in ad libs. Since part of the ad lib involved the main trio transforming and making a performance (driving away the water demons), the rest of the play had to be improvised.
Thanks to this trope, in the Slayers universe it is assumed that anything that occurs on stage while a play is being performed is part of the play. That includes spontaneous script rewrites, duels with real swords, and massive explosions. Lina and Co. got an award for their ad-libbed play (which, while completely nonsensical, was much more entertaining than the original story they intended to perform).
In the Ace Attorney manga, during Turnabout Showtime, after Flip Chambers, who plays Twinklestar in the Sparklestar show for Sparkle Land, is stabbed inside his costume, he comes out on stage as scheduled before collapsing and dying. Toward the end of the trial, Phoenix speculates that "Maybe he thought the show must go on. Or maybe he was asking for help."
Similar to the Mermaid Melody Pichi Pichi Pitch example, Yes! Pretty Cure 5 had an incident early on. Urara is chosen to be the MC for a kid's play, but it turns out that the actress playing the rabbit fell ill. Nozomi, not wanting her friend's big day ruined, takes up the role of the rabbit... despite Rin pointing out that she was banned from the Drama Club after only 3 days in. Despite this, they go with it and things start out alright... only for Girinma to arrive and summon the Monster of the Week. The girls are able to blind most everyone to transform and the audience is treated to a Pretty Cure fight... which is a big hit with the crowds. When Urara's manager approaches Urara once more and wants the same thing to happen, the poor girl's left in a bind, while her friends tell the audience their answer:

Nozomi, Rin, Komachi and Karen: "Not going to happen."

Fairy Tales

The Emperor's New Clothes: What's the Emperor to do when it's revealed his marvellous new clothes don't really exist and he's naked? Pretend not to have heard the complaint, hold himself up stiffer and straighter than ever, and continue with the procession, that's what.

Film

The Marx Brothers A Night At The Opera where the brothers throw an opera into total chaos and the theatre crew and police still bend over backwards to avoid disrupting the show themselves, even when things are bad enough that logically they might as well simply and openly march out on stage to grab the brothers since it would not make any difference.
Galaxy Quest:

Jason Nesmith: You will go out there.
Alexander Dane: I won't. And nothing you can say will make me.
Jason Nesmith: "The show must go on."
Alexander Dane: (Beat) Damn you. Damn you!

In Moulin Rouge, Satine is dying from tuberculosis and everyone's hopes and dreams are falling apart, but they still manage to stage "Spectacular! Spectacular!" Guess what The Song Before the Storm is?
The Adventures of Sherlock Holmes' Smarter Brother: Sigerson Holmes and Professor Moriarty (and their minions) engage in a secret contest behind the scenes of an opera performance to get some important papers. Their shenanigans include dropping sleeping pills into the cups the actors are drinking from, firing guns and breaking into song: the actors try desperately to keep the opera going despite the interruptions.
Lampshaded in Shakespeare in Love, apparently set before the phrase was popularised:

Henslowe: The show must... you know...
Shakespeare: [prompting him to continue] Go on!

A more tragic case in Stage Door; on opening night of her debut, Terry finds out Kay, an actress she was friends with, had her heart set on the part Terry was about to play, and when she didn't get the part, committed suicide. Upon hearing this, Terry is heartbroken and refuses to go on; Ann Luther, her acting coach, gives a variation of this speech to get Terry to perform.
In Henry's Crime, Henry goes back on stage and continues his role as if nothing's wrong, immediately after getting shot in the leg. Justified because if he hadn't, it would have aroused suspicion.

Literature

The name of a chapter in a The Berenstain Bears book in which Brother and Sister bear attempt to help a horseback riding teacher save her building by means of a fundraiser to pay the mortgage. In the chapter, the villains have been defeated and prevented from sabotaging the fundraiser in their bid to gain control of the building, but despite the problems they have, they still have to hold the event to get the necessary money.
In Maskerade, this is the philosophy of the Ankh-Morpork Opera House, where a show cannot stop even if the lead singer is dead (they recruit another from the audience, or work the corpse via ventriloquism). When someone actually does stop a show (as it's Discworld) the resulting entropic shockwave physically flings Walter Plinge, a man truly in tune with opera, from his seated position.
This is Rachel's motto in No More Dead Dogs, even as early back as kindergarten. At the end of the book she convinces everyone to remain performing the play with these words after the Old Shep dog is blown up with a cherry bomb.

Live-Action TV

A standard trope in The Muppet Show whether it is using a petrified Ms. Piggy as a prop or shoving a wardrobe on stage with the guest star, Chris Langham, trapped inside to sing "Hawaiian Cowboy" (complete with a cowboy hat on top of the wardrobe).
- One exception is when during the Glenda Jackson episode when Kermit can't take anymore and goes on stage to say "They say the show must go on, but they never explain why. The show's been taken over by pirates, the theater's sailing out to sea and I'm losing my mind..."
The entire show Dark Shadows. What is that lurking in the dark shadows of Collinwood manor? Is it a ghost? A vampire? or is it just the sound man again?
The British soap Crossroads. Someone flub a line in dialogue? Did the other person flub a line right back? Did a piece of the ceiling fall down during a scene? Is that a boom microphone two inches from Sue Hanson's hair? There's no time for editing!
Whose Line Is It Anyway? of course typically plays through any missteps but the show also has a game built on this trope where the players are in a theater production and all but one of them (typically Colin) have dropped dead leaving the one living player desperately trying to continue the show dragging around the corpses of the other players.
"Ham Radio," one of the funniest episodes of Frasier, is all about this trope. Frasier tries to do a live radio drama, and his tyrannical direction leaves him with a cast of Bulldog, stricken with stage fright; Roz, who has an emergency root canal just before the performance; Gil, who is determined by hook or by crook to say his character's big speech when Frasier decides to cut it; Bulldog's dyslexic girlfriend; and Niles as the rest of the characters, which Frasier neglects to tell him until the show has already started. Add in some rather unfortunate sound effects and you've got one whopping Crowning Moment of Funny.
In the Pilot of Thirty Rock, a TGS sketch went south while Liz was away meeting with Tracy. When they arrived in the middle of the fiasco, Liz told him to go onstage and talk about "anything", which he did.
In Glee, during the sectionals, they find that someone leaked their setlist and that the other two teams, who were performing before them, had copied their songs. They realised that if they went with that setlist they'd be accused of cheating, so they end up having to pick, practice and choreograph four new songs in an hour. Of course, they still win.
One story arc on Schloss Einstein had the sixth-graders putting on a production of Die Räuber. The kid who's playing Karl gets sick right before the performance, which leads to the brainstorming of increasingly ridiculous ideas to save the play (the replacement Karl has no time to learn the lines, so they try pinning a copy of the script to another kid's back, for instance). They finally realise that Lilly, the prompter, knows the entire text by heart, so she goes on as Karl and saves the play in spite of her incredible shyness.
- This was also subverted in a later episode. We don't get to see it, but apparently a similar thing happened at Liz and Annika's old school:

Feli: What's this [picture]?
Liz: A theatre performance. I was the circus princess.
Feli: And Annika?
Liz: The prompter. The clown had broken his leg. Annika was the only one who knew all his lines by heart.
Feli: So she took on the role and saved the performance!
Liz: (shakes head) She totally panicked. She actually got sick!

In the Parks and Recreation episode "Telethon", Detlef Schrempf was supposed to appear on a diabetes telethon, but he and Tom ended up getting sidetracked at a bar. Meanwhile, the rest of the gang had to come up with alternative forms of entertainment, which included Leslie performing a riveting game of flip the coin:

Leslie: Heads. Oh boy, what is going to happen next?!

On The Daily Show, when Jon Stewart cut his hand (though not badly).
Jim Henson had an American Bullfrog urinate on him during a Sesame Street lecture. Jim was not unseated; he was controlling Kermit the Frog at the time, and only lost enough control of Kermit to make him snicker. Kermit said that the frog had "told a funny joke."
In Buffy the Vampire Slayer, Sunnydale High School holds a talent show...while a horrible demon looks for organs to become fully human. The curtain happens to open just after the demon is decapitated by a guillotine while the main characters are all gathered round. The crowd is dead silent...

Principal Snyder: I don't get it. Is it Avant Garde?

In The Mary Tyler Moore Show, the station pledges to do an all-nighter live broadcast about the mayoral election until the decision is made. Unfortunately, a blizzard cuts off their connection to the voting booths after the first set of numbers come in, leaving everyone to flounder desperately for something to do until they can somehow get word of who won. The best part comes when Ted completely runs out of ideas and just stands in the studio, doing and saying nothing. "I don't believe I've ever seen that before."
Family Feud host Richard Dawson said in an interview that he absolutely hated stopdowns, and would demand that the staff work around anything that they possibly could. This led to such oddities as the Fast Money round being played on cue cards because the electronic board went on the fritz.
A Jeopardy! contestant once fainted during Final Jeopardy! Because stopping tape might have affected the outcome of the game, the contestant was roused and asked to write down his response. The entire incident was left in.

Music

Queen lead singer Freddie Mercury contracted AIDS and was in increasingly poor health through the last few years of his career. He kept recording though, as, well you know. The band lampshaded it with an absolute Tear Jerker of a song named, unsurprisingly, The Show Must Go On. Also qualifies as a Real Life example.
Averted by Emilie Autumn, who would pause shows if something went wrong on stage.

Professional Wrestling

The WWF suffered this trope in 1999 during their Over The Edge pay-per-view event, due to the death of Owen Hart happening as he was making his ring entrance.
This actually happens often in professional wrestling. The most common causes are legit injuries and/or botched moves, or in rarer cases, botched use of props, weapons or equipment.
We'll say that professional wrestling is like this in general. As Cracked.com articles such as 5 Reasons Pro Wrestlers are the Best Actors in the World put it, a wrestler is supposed to stay in character no matter what happens. Your opponent is legitimately trying to injure you? Ignore it and stay in character. You tore your ACL? Broke your ribs? Don't break character. One of the competitors died during the match? You can't even let that break keyfabe.

Theatre

This is the entire plot of Noises Off.
The plot of Curtains kicks off when the star of a musical in tryouts in Boston is murdered after a performance. The rest of the cast plan to go back to New York, and one of the producers tries to get them to stay for the rest of the preview period by singing "The Show Must Go On," but the actors are not convinced. It isn't until the detective on the case reminds them that they're "Show People" that they decide to stay.
Subverted catastrophically Pippin. When Pippin refuses to perform the final scene of the show (which has No Fourth Wall), the Players try to exhort him to continue, with remarks like, "Hey, you're not going to disappoint all these people at $25 a seat, are you?" But when they see that Pippin is firmly determined not to commit Self-Immolation, they retaliate by taking away the lights, costumes and makeup. The Leading Player apologizes to the audience that the promised finale cannot be presented, offers the part to anyone in the audience, and then orders everybody out, including the orchestra, leaving Pippin, Catherine and Theo to end the show on a denuded dark stage.

Video Games

The opera in Final Fantasy VI gets completely derailed when the party and an enemy end up crashing down on it from above. They end up improvising completely non sequitur roles on the spot. Hilarity Ensues when the theater owner decides to Throw It In and has the orchestra cue up the appropriate music.
- By completely derailing, we mean a treasure hunter and two companions which may include the king, a feral teenager, a ninja, and a samurai, fighting an octopus, using powers believed to have vanished a thousand years ago, in the middle of a tragic love story, concluding with the female lead (played by a general of a rival nation's army) being abducted by the pilot of a zeppelin.
Final Fantasy IX features a circumstance VERY similar to the FFVI example above in the opening sequence, when the main character's Thieves' Guild disguise themselves as an acting troupe performing the most popular play in the world as a guise to kidnap Princess Garnet. When Zidane, Garnet, and Captain of the Guard Steiner find themselves on stage in the midst of the production, Hilarity Ensues as they take the plot Off the Rails entirely in their bid to escape. And the Queen still loves it!
Baldurs Gate 2 featured the start of a character recruitment quest happen at a theater where a recruitable NPC was kidnapped prior to the show. True to the trope, Biff the Understudy steps up to fill the role and delivers a wooden, stuttering, uninspired and all-around dreadful performance.

Western Animation

Played for laughs in the King of the Hill episode where Bobby inherits a famous ventriloquist's dummy that was modeled after a stereotypical football-playing high school A-student... only to become dismayed when his father likes the dummy's "antics" more than Bobby's own. Bobby grows to hate this new attention, but mutters "the show must go on" when he realizes that being at the edge of the spotlight is better than not having attention at all. (Luckily, the trope is kinda subverted in the end when Hank isn't a total bastard - after the first dummy is destroyed, he decides to nurture Bobby by building him a new dummy that far more resembles the boy himself.)
In the Animated Adaptation of Madeline and the Gypsies, this is the reason the Gypsy Mama gives for putting Madeline and Pepito in a lion costume (as the real lion is sick).

Real Life

During a 1973 concert in San Francisco, drummer Keith Moon of The Who passed out due to a drug reaction. Rather than stop the show, the band recruited an amateur drummer (the late Scott Halpin) from the audience to replace him and finish the show.
Similarly, a 2002 performance by Counting Crows in Los Angeles saw drummer Ben Mize fall ill mid-show, requiring his hospitalization. After a brief intermission, the band switched to acoustic instruments and performed several songs without a drummer, before drummers Randy Guss of Toad the Wet Sprocket (their opening band) and Todd Roper of CAKE (who was in the audience) were persuaded to appear onstage to finish the show.
Naturally, anybody who has appeared in live performances can testify to problems involved in cast members, problems with props or any number of unforeseen difficulties. The universal rallying cry is, in all circumstances, the Trope Title.
Comic Red Skelton, on a live 1950s show, was doing a sketch with a cow, which started defecating, for a very long time. Needless to say, the audience was in stitches, and Red spent the interval pulling faces, holding his nose, and telling the cow "No ad-libbing!"
On an episode of The Honeymooners, recorded live, Jackie Gleason was supposed to enter the scene but, for some reason, didn't for a couple of minutes. Art Carney, alone on stage, filled the time getting an orange from the refrigerator, peeling it, and managing to make it funny.
Reportedly, when recording "The Show Must Go On" (mentioned above), Freddie Mercury was in seriously bad shape because of his battle with AIDS. One of the other band members approached him and asked him if he wanted to take a break. What Mercury did was down a glass of vodka and say "I'll fucking do it, darling!" before proceeding to nail the song in one take in what Brian May considers one of Freddie's greatest performances.
Before opening night of Rent, composer Jonathan Larson collapsed and died. Needless to say, the cast moved on to perform the next night.
- What's more, when the cast was told, they decided to pay their respects by just singing through it seated around a table. By the time they got to "La Vie Boheme", everyone simultaneously agreed that Jonathan would want to see the show as it was meant to be, got up, and did the entire rest of the show, sans costumes.
When a member of one of the Big Name Bands headlining at the Download musical festival fell ill on the night, members of several other bands performing at the festival stepped in to take his place for the set list, to prevent a possible riot if one of the bands that almost everyone wanted to see didn't perform as scheduled.