1. Iron Man
How Would It Change The Franchise?Hugely. Robert Downey Jr. has been the center of the Marvel Cinematic Universe. His Tony Stark is what made this all possible and he commands so much weight with Marvel that he was able to fight for higher paychecks for his co-stars. But his contract is only for two more films, and Downey himself has said he can't go on playing the character for much longer. Like it or not, Downey is going to bow out soon, and the third Avengers film will likely be his last. And he might only have flashback appearances in that, as characters are reminiscing about him while dealing with the fall-out of his death. Plus, rumor has it Stark will create Ultron, so what better synergy than for the creation to kill its creator? That would be hugely impactful for the Avengers and for the audience as well. And it could mean Don Cheadle's Rhodey stepping into the armor to honor his friend.
Will It Happen?I've said before that Tony Stark will, at some point, need to be recast. Sorry fans, but it's inevitable. James Bond went on without Sean Connery, Batman went on without Michael Keaton, Superman went on without Christopher Reeve, Spider-Man went on without Tobey Maguire, and Iron Man will go on without Downey. And there's nothing wrong with that, so long as they get a good actor for the role. But one thing I've also said is that, to make the transition less jarring, giving Tony Stark a break for a few flicks would be a good idea. And one way to do that would be to kill him off and reveal in a post-credits sequence that he's still alive while Rhodey steps into the suit for a few movies.