Iron Man/ Tony Star is an INTEGRAL part of the whole Marvel Cinematic Universe. He is the beginning (Iron Man, 2008). He is in Avengers 1 and 2. He provides resources and technology to the Avengers. If he is gone, I would really doubt that if the MCU can hold together. It seems to me that Iron Man is questionably the most popular avenger. He has the broadest appeal. So I think he's going to be in, at least, avengers 3.