At this point he is just about an adult so a year of Prep in some remote location with good people, where he can sever the bad influences could be his last chance. Hopefully he's got some interests other than basketball so he can become a real human being regardless. Distance, perspective and developing a deep appreciation for higher values and goals is what can get you there. I did this twice as a young person who had gotten into some trouble and recidivised before heading to St John's after cutting ties with loser "friends" I actually got expelled my senior year of hs about a month before graduation. Fortunately I got my St John's acceptance letter just a couple of days later!