I don't think that he should veg out for unlimited hours playing games.
He should be required to do what he's capable of doing. But, I cannot determine what that is. An illness, mental or physical, is not an excuse for sloth.
I would discuss this with the doctors and come to an agreement about what he can and cannot do. He will have to care for himself one day. Enabling him will not help him.
Wishing you all the best. I know this is difficult.
Shalom!