Keep in mind how Tony crashed in the Iron Man suit prototype he built in the cave and he survived a pretty severe crash inside of it. He also survived numerous -unprotected- crashes testing out various elements of the Mark I suit/the "real one."
We're dealing with comic-book physics here. Tony was also able to produce a brand-new, highly-powerful element in his basement
So, yeah, I'd say he just "somehow" survives the impacts while in the suit.