Overall slower functioning (movements, speech, etc.) or problems with short/long term memory are two examples, but the doctors or anyone else hasn't brought up the possibility yet that there will be long term damage.
What it sounds like to me during the first 24 hours they were worried about the swelling, I don't know if any of you fellow Americans remember that girl that got hit in the head with a hockey puck during a game a few years ago, she seemed to take it alright and even walked away from the scene but within hours she died because of the massive swelling. I think that is why the doctors were so concerned for the first couple of hours, but the hamster has gotten through that now.
So hopefully he is on his way to a full recovery.