Saved by Canon

"Yoda: Kill you, I cannot! But kill me, YOU cannot!

Emperor Palpatine: Because we are equally-matched opponents on opposite sides of the same almighty Force?

Yoda: No, because already released have the sequels to this movie been! And in them we both appear! Problem this is with prequels - no suspense can there be when already we know which characters live!"

- Mad Magazine's parody of Revenge of the Sith

In that last movie you watched, or the last game you played, there're maybe some epic and great battles between two or more characters fighting to the death and one of them seems to be on his last leg, or maybe one of them seems to about to die by being poisoned by something, or maybe they're about to fall of a cliff and hit the ground below, or maybe they're about to crash in the middle of a carchase. Whatever the case, you know that they'll survive because if they die, the fictional works that takes place chronologically after wouldn't be able to exist in the first place then.

This trope usually exist in prequels and Interquels. In them, characters from the original material usually appears on their younger ages, and like the new characters, they usually are forced to fight deadly battles against the enemy, and many of those battles are as nasty and brutal as they come, and many of them seems to result with the old characters dying and the villain laughing his ass off in triumph. But you know that whatever convincing they may try to make it look like, they're still alive and will not die since if they did die, the original stories that came first may end up with the Canon Dis Continuity stamp on their heads.

Constast Doomed by Canon, when the characters are going to die no matter what because the original works said they died some time before the story takes place.

General

 * Trailers Always Spoil: It's generally not a good idea to look up a continuation of a series if you still haven't experienced all of the current installments. Simply seeing the trailer for a series can spoil you by detailing which characters survive.

Comic Books

 * Any tale of Wolverine's past will have the same prepared answer to the question of whether Wolvie's going to make it.

Literature

 * In an interesting example of a character being Saved by Canon for the moment, but Doomed by Canon in the long run, T'Prynn in the Star Trek Vanguard novels can't die, even when she's in a coma due to Mind Rape ... because she's going to die in a transporter accident eighty years later, as shown in Flash Back in the Star Trek Deep Space Nine Relaunch novels.

Film

 * In Revenge of the Sith, the duel between Anakin and Obi-Wan ends with Anakin losing both his legs, savagly burned and left for death by Obi-Wan. If you watched the original Star Wars movies, you know that Anakin will survive since if he died, it would mean no Darth Vader.
 * In X Men Origins: Wolverine, it look like Wolverine is about slam his claws right in Sabretooth's throat. Granted, he just knock him unconscious but you already know that he wouldn't kill Sabretooth anyway since he appeared in the first movie, that takes many years after this movie.
 * In Bambi 2, it looks like Bambi has been killed when he fell of the cliff after the dogchase, but you already knew he survived since the first movie has him growed up to an adult. Still a pretty effective scene though.
 * In Terminator Salvation, we already knew that Kyle Reese would survive Skynet because without him, no Terminator movies. However, in the original, unused ending would've subverted this trope:

Video Games

 * Since Kingdom Hearts Birth By Sleep takes place ten years before the first game, you know that most of the bosses will survive after you defeated them, especially Maleficent and Xehanort.
 * In The Force Unleashed, you already knew that neither Darth Vader or Emperor Palpatine would die in their duels with Galen Marek, or that none of the rebel leaders would be executed by the Imperials since the game takes place two-six years before the original trilogy.
 * In Final Fantasy VII: Crisis Core, Sephiroth, Aeris and Cloud are gonna survive no matter what, since if they died, then it means that the series' most successful game well might not have existed in the first place. however is Doomed by Canon.
 * Metal Gear Solid 3 Snake Eater lampshades the survival of Revolver Ocelot by calling you out on creating a Time Paradox if you actually do kill him.