As of right now, Robert Downey Jr. has a contract with Marvel to appear in Avengers: Age of Ultron and The Avengers 3. Beyond that, we don't know what will happen with him. A lot of fans are wondering if he would be willing to come back for a fourth Iron Man film, and you'll be happy to hear that he's still open to the idea of doing it.
Marvel Studios president Kevin Feige has confirmed that Iron Man 4 will happen, and Downey Jr. was asked in a recent interview with EW if he would reprise the role or if it would be recast, and this was his reply:
“It’s down to Kevin Feige and Ike Perlmutter and Disney to come to us with what the proposal is, and that’s on us to agree or disagree. When things are going great, there’s a lot of agreement."
The actor is pressed for a little more information, and it seems like this is a role he isn't really ready to give up saying:
"It’s that thing of: why give up the belt when it feels like you can barely get jabbed? Most people are saying that right when they get knocked out."
It sounds like there's potential that things could all work out in bringing the actor back for more Iron Man action! This makes me happy because I'm not ready for Downey Jr. to not be Iron Man.