Convenient Terminal Illness

So something bad is about to happen; a nuclear weapon is about to go off, or an asteroid is about to impact the planet and the only way to avoid this is if someone stays behind and sacrifices himself to stop it. But who will go? All of these characters are life long friends. There's no easy way to decide. Or is there? One of the characters has an Incurable Cough of Death and only a few months to live. He'll do it - after all, he's dying anyway, and in a far less dramatic and spectacular way.

This trope is about when a character gives his life for something based on the reasoning that he's going to die soon anyway. It's a favorite for when a writer wants to make a bittersweet ending less bitter.

Occasionally, the doctor will burst in just a second too late to explain that he tested the wrong vial and the character isn't (wasn't) going to die. Oh well, it's too late now!

Compare The Last Dance.

Anime and Manga

 * In Fullmetal Alchemist, the same character does it in two different ways.
 * In The Conqueror of Shamballa, The Movie of the first anime, Hohenheim does this incomprehensibly.
 * In the manga and Brotherhood adaptation, Hohenheim  since his ontological inertia has been broken down in the battle and he is dying anyway.
 * Naruto: Played straight with Kimimaro, who dies with his weapon just centimeters away from piercing Gaara's eye.
 * If he was that fast and strong when he was dying of terminal illness, then think about how fast and strong he was when he was healthy.
 * Subverted later in the Sasuke vs. Itachi fight. Itachi appears as though he's about to kill Sasuke, when he keels over dead after coughing up copious amounts of blood throughout the fight. But then it's revealed that . Especially convenient for anybody standing in Itachi's way; when he was healthy, he completely wrecked two of Konoha's strongest shinobi without breaking a sweat.
 * Darker than Black (the first season), when and chased by Syndicate thugs. Cue a car chase with fireball as the "prize".

Comics

 * Early in the X-Men comics, Professor Xavier died. Then he returned. It was explained via flashback that a terminally ill mutant scallywag calling himself the Changeling offered to pose as Xavier so the Prof could prepare for an imminent invasion. Jean knew, so as to help the shape-shifter better pass off as the X-Men's mentor.

Fanfic

 * In MGLN Crisis,, according to Shamal, have about a year to live. They make a Heroic Sacrifice toward the end of the fic.

Literature

 * An example where we find out after the fact: In The Dresden Files (Death Masks), Harry is being held in a completely inescapable position by the Dangerously Genre Savvy Nicodemus, who offers him a choice between joining him or being killed. That's when barges in and  A couple weeks after everything goes down, Harry gets a letter in the mail:  had terminal cancer and only a few months to live.
 * After at the end of Harry Potter and The Half Blood Prince, we are informed in Deathly Hallows that   Interesting in that the character is not revealed to have been critically ill until after his death.
 * In The Guns of Navarone Stevens got gas gangrene and had to be dragged along to prevent Germans from capturing and interrogating him. So when they are chased he pulls a gun on the others and insists on being left behind to cover the retreat and take as many enemies as he can with him.

Live-Action TV

 * In 24, CTU Director George Mason gets a fatal case of radiation poisoning while searching for a nuke in Day 2. At the end of the Day, Jack flies an airplane carrying the nuke on a suicide course to the desert to prevent it from killing anyone only for a stowaway Mason to reveal himself, convince Jack to not throw his life away and take his place at the controls while Jack parachutes to safety.
 * It also helps that while Mason was dying, he looked back on his life and realized how much he had made everyone close to him dislike him, which caused him to try make amends with his remaining time. Being poisoned not only gave him a reason to sacrifice himself in another's place (he says that he'd rather not suffer the end stage poisoning effects), but most likely was why he would even consider doing so.

Movies

 * At the end of Gran Torino when
 * The entire point of Joe Versus the Volcano, with a twist:.
 * Played with in Madagascar: Escape 2 Africa with Melman also going to jump into a volcano.
 * In Repo! The Genetic Opera, Rotti Largo is told that whatever illness he has is terminal, so he sets the movie's plot in motion, namely . He dies at the end of the movie.
 * Near the beginning of Space Cowboys is told he has pancreatic cancer with only eight months to live. Naturally the only way to save the world from  is for somebody to   and since he is dying and going there has been his lifelong dream, guess who volunteers.

Video Games

 * In Final Fantasy X, Seymour's mother indirectly cites this as being part of her willingness to . Uniquely for this trope, it manages to backfire spectacularly, because what any outcast Half-Human Hybrid needs is for his mother to lay the weight of saving the world on his shoulders as she kills herself/leaves him forever. Is it any wonder he winds up a Woobie, Destroyer of Worlds?

Web Comics

 * In Gene Catlow, . It doesn't end well for him.