Avengers: Annihilation
In the comics, Avengers: Annihilation is a 2006 crossover event that saw the galaxy’s greatest heroes unite to stop the alien Annihilus from releasing his devastating Annihilation Wave and laying waste to the cosmos.
Now, obviously, there’s no way that this specific story could be adapted for Avengers 4. For one, it’s unlikely that a new villain would be introduced in place of Thanos when the Avengers have still to properly deal with him. More pertinently, Marvel Studios don’t even have the rights to Annihilus, as he’s tied up in the Fantastic Four universe that currently rests with Fox. Plus, James Gunn has already called dibs on him, anyway.
What could happen, though, is that Avengers 4 uses the title of story in name only. After all, that would still be a pretty apt moniker for a film that deals with half of the universe being wiped out and the heroes themselves facing extinction. The big piece of evidence for Annihilation being the title, though, is that the Russos have said that Avengers 4‘s real name should scare us.
While this is certainly a possibility, it would probably still be better to save the title and deliver a more faithful version of the storyline once all the pieces of the puzzle have been reclaimed from Fox, when the Disney merger goes through. As soon as the likes of Galactus and Silver Surfer are back in play, then this would be a fantastic idea.