Thing is, RDJ doesn't have to be Iron Man to be Tony Stark, and Tony doesn't need to be around to have Iron Man. Same with Rhodey, Cap, Falcon etc. They can kill of the actors and the people, but still have the characters remain, existing in the same universe with different people. You could have people retire and someone else bring up the mantel as well. There are a lot of different avenues that can be taken to eventually weed out the current cast, possibly bringing some back in the future, and stil continue the overall plot of the universe. It'll be odd at first, and there will be much scrutiny over how they go about those things, but I don't think it'll be a big deal in the end. This thing could go on for a long time.
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