Will there be a character's death in part 3?
Coulson died in part 1. Who knows how the stakes will be raised in part 2. But for part 3, the stakes should be raised further. Will this be a hero's final appearance, will they sacrifice themselves or be killed outright? I guess we'll see.
I see Downey as Iron Man retiring the role after part 3. In all likelihood, there will be a near-definitive death, but there will probably be some backdoor plot thread like uploading his consciousness into a computer, or Asgardian science possibly preserving the body.