Things can change very quickly w/a person in crisis. For now, I would put the idea of broaching the subject of going out for the evening aside. If his family should offer to watch your son while you are there, then that would be the time to say, "hey, do you want to catch a movie or go out for a bite to eat?" However you handle this, you need to pose it as a question that he can decide what he wants to do.
If you say something to him now, he will think that you and his family are conspiring against him, i.e., putting pressure on him to conform to the old him and/or making plans w/o his input.
Just my two cents.
Sit quietly, the answers will reveal themselves when you least expect them to. The past is gone, the present is a gift and you need to focus on today, allow the future to reveal itself when it is ready.
