In a recent interview, Joss Whedon announced that he will not direct Avengers 2 unless Robert Downey, Jr. returns as Iron Man.
“He is Iron Man in the way that Sean Connery was James Bond. I have no intention of making Avengers 2 without him, nor do I think I’ll be called upon to do that. I don’t think it’s in my interest, Marvel’s interest, or his interest, and I think everything will be fine.”
You can read the interview here.
Avengers 2 is expected to start shooting early next year with a release in 2015.