Chuck Liddell had the same questions about Kurt Angle when he was "angling" for an MMA career: how will he react when he gets hit? Well, with Brock, now we know.
The question is, will he take pains to spar so that he can develop a tolerance to the pain? If he is willing to do so, he has a chance to become champion again. If not...
The gap in the skills isn't as big as some make it out to be. The huge gap that I saw was in their mental game. And in theory the mental aspect of fighting can be improved on a lot quicker.