With [Guardians of the Galaxy 2](movie:1081113) ready to hit the cinemas in 2017, 3 years after the first there is a possibility GOTG 3 could start off Phase 4 in 2020, a year after Avengers: Infinity Wars Part 2. What this means is Robert Downey Jr. would have starred in 8 films as Iron Man (Iron Man 1,2,3 - Avengers 1,2,3,4 - Captain America 3) meaning that he may still do one, two or even more films as he had said earlier this year, "You know, it may verge on double digits. But it will probably wind up being a little shy." - RDJ.
His statement got everyone excited and curious on what will happen in Phase 4.
If the number ends up being shy of double digits it means Downey Jr. will appear in only one movie after Infinity Wars Part 2. That movie could be [Iron Man 4](movie:886190), another film like Civil War caused by the aftermath of Infinity Wars Part 2 or it could be my favourite one, a team up with the Guardians of the Galaxy. I mean come on Iron Man, Star Lord and Rocket in space kicking ass is all marvel needs to go past Avatar in money earned. This team up would even beat a Spiderman and Avengers team up, ok maybe not after all it may actually happen with the help of the petition but without Andrew Garfield, no way he's too good. Anyway getting back to the matter at hand, Iron Man with the Guardians could have something to do with Infinity Wars Part 2 aftermath, cleaning up, disposing of Thanos or anything that works. In this adventure Iron Man could used very differently as opposed to on earth where he knows everything and can handle himself, in space he could be vulnerable and need guidance which would create great depths and dynamics to the image of Iron Man and more importantly Tony Stark. If this is RDJ's last movie as Iron Man, he could be killed off and retired which wouldn't seem too ridiculous in space or be replaced for the future by some new actor who would gain sympathy and much less backlash from fans.
If RDJ decides to carry on for a bit longer his next movie should NOT BE IRON MAN 4, I know 'say what?' Well the reason for this is that we would have already seen Iron Man focused on in GOTG 3 and Iron Man 4 would most definitely be THE END for him while focusing on him solely, to much pain! Ending RDJ's run in Avengers 5 is the best and grandest way to send off the CREATOR of the Marvel universe. It's better to kill him off in the most heroic and emotional way possible as it will mark something in Marvel's Cinematic Universe or retire him with Pepper Potts, replacing seems very likely and appropriate but common the poor guy taking over him is basically doing career suicide. RDJ as Iron Man is too beloved to be replaced. Avengers 5 should also mark the end (Retirement is best for most) of all veteran Avengers, Iron Man, Cap, Thor, Hulk, Black Widow and Hawkeye, letting the new heroes of phase 3 takeover and win hearts. The villain will have to be someone big and powerful even if not popular as a Thanos or Ultron.
If Robert Downey Jnr. does touch 10 films as Iron Man he should not be replaced but retired or killed as it technically is the only appropriate way, I mean the 2012's Avengers are not going to be younger in Avengers 5 which could hit screens all the way in 2025 to later.
GUYS REMEMBER THIS IS ALL SPECULATION PERSONALLY BY ME ONLY