I am so sorry. My son is still in Residential Treatment Center (RTC) but we have watched kids leave there with that same adamant attitude, who have not done well since, and I completely fear the same result.
I am not sure whether it is within your family's means, but have you considered placing him in a therapeutic boarding school (TBS)? It is a remedy of last resort for a lot of families, but maybe will give him the chance to grow up.
Which is the way I now see the issue my son has. Since my last post, I have read a couple of books my Johm McKinnon, who founded one of the first TBSs. In a nutshell, he has seen hundreds of troubled teens with a host of different behavioral, substance abuse and personality issues, and multiple diagnoses, but has identified a common thread among them -- they are stuck in "relative immaturity" in comparison to their peers.
It's worth a full read but this from his first book The Unchanged Mind... made me go "that's it."
Ticking off these element on my fingers I explain that at home, before parents made the decision to take action, each of our students: • Thought only of himself, his words and actions demonstrating little consideration for parents, siblings, teachers, or anyone else except his pals-and often not even his pals; • Seemed incapable of empathy except for the close friends she considered to be "just like me"-and certainly not for anyone she considered to be unlike herself; • Treated parents and girlfriends like puppets whom he had a right to expect to do his bidding-to pay for him, to wait on him without thanks, to exercise no independent judgment, to take seriously no motive apart from his wants, to enjoy no right to separate wishes or a distinctive point of view-so that if a parent or sibling or girlfriend said "no" or tried to go her own way or to express a different opinion, he felt he had the right to throw a tantrum, argue, threaten, badger, or punish-or else felt entitled to sneak around or defy any prohibition; • Considered it all about now, leaving the future a hazy, unimportant destination disconnected from the present, where (insofar as she bothered to imagine any goal) she expected to arrive by means of wishful thinking; and • Was willing to manipulate or sneak around or to cheat or steal or dissemble or mislead so as to get his way or to get something he wanted; and, although also open to all available rewards, he was inwardly restrained from defying a prohibition only by virtue of his calculation of the odds of getting caught and punished.