Re: Downey's last?
Why do so many fans assume that these characters must die after a few appearances? Iron Man's 50th anniversary is this year and it's safe to assume that he'll be around for at least fifty more. Why would Marvel kill off its most popular character (in the MCU)? Because he's played after three solo films? That's hardly the case.
Tony Stark has fifty years of history to mine for new cinematic adventures. There is no need to kill him off when he has so many possibilities open for exploration.