The tough stuff is the recovery. He'll be sore as you well imagine. Probably moreso from the harvesting done on his legs than anything. He'll be scared of coughs and sneezes for quite a while. He may have some panic set in from time to time. It's normal.
If you get a chance, tell your Mom to let all his buddies know the best thing they can do is wait a week or so after he gets back home and then set up a schedule for them to come sit with him for a few hours a day while your Mom gets a break. He probably won't want to be alone for very long and she's gonna be worn slam out.
Also, it'll be interesting to watch the changes that will come over him. He's never been more in tune with his own mortality than right now and the next several weeks. He'll probably be more emotional than you've ever seen him. And he'll probably be noticeably different in some ways after this experience. After he gets through the recovery, he'll be a new man. You'll be amazed.