RandV
It's a wolf v2.0
I still think it's Captain America's destiny to take the fall.
Then again, they've built him and Iron Man up as co-leaders of the Avengers so it would leave Stark feeling pretty guilty if Rogers sacrifices himself alone.
At the same time, Tony Stark is perfectly placed for cameos unlike Rogers who is really more of a soldier. Downey Jr. can appear in other people's movies as a patron or rich philanthropist and give those films instant credibility and fan service. He would make a mint just for a few minutes of screen time.
Meanwhile, I think Chris Hemsworth would want to keep the Thor train running as long as possible.
With Hulk, I'm wondering if they could just swap in a different Banner (kind of like Rhodes) if Ruffalo isn't interesting in doing it anymore.
Yeah I revised my thinking about after posting that. I was going with the idea that Nick Fury has to show up in Europe and recruit Peter Parker because he doesn't have anyone else at the moment, but wasn't thinking about the actors themselves wanting to continue their roles. So from the original cast I still think this holds true for Stark and Rogers but Thor isn't necessarily on Earth to be called, Hulk isn't reliable, and by themselves Black Widow/Hawkeye are agents, not heavy hitters.