His poor son. You didn't mention his age, but I'm guessing HS-college-age. I don't think I'd lift a finger to do anything more for the ex, but if you have a way of contacting his son, maybe you could suggest Al-Anon for him.
I think you were very kind, and I might have done the same as you. I definitely would have talked to the son (and good advice you gave him, too), and maybe I would have even done the "drive to rehab."
I'm glad you don't have to deal with it every day anymore, too.