I've never understood the mentality which would judge a character's presence on a team based on something like power levels. As soon as you do, you have to start drawing arbitrary lines in the sand as to what makes who worthwhile. If the team has Thor, it really doesn't need Iron Man, Cap, Black Widow or Hawkeye because he can do more damage and is more powerful than all of them combined. The point is that these characters are people, individuals who contribute more than just a power set. The whole point is that the team is more than the sum of its parts, so the sum of the parts aren't relevant.
On a side note, I think that given that Iron Man 3 is the last film RDJ is contracted for, it could be pretty powerful to kill him in an Avengers sequel and never risk over saturating an audience on RDJ's Iron Man. That said, I'd be perfectly happy with no deaths.