Re: Downey's last?
There's no doubt in my mind that RDJ will appear in Avengers 2. The finality of Iron Man 3 has me doubt anything beyond that though.
I hhhhhate the idea of recasting. Honestly I'd rather see Stark killed off (Joss loves doing that), or at least gracefully retired. There's enough characters in Marvel's roster to keep them going for decades with or without Stark. The film universe can't exist like the comics do, actors age and the characters should too. There's also only so many films that can be made at a time. If Marvel continue to layer in fresh characters among established ones there's so many opportunities.