I believe you need professional advice not opinions from a bunch of kids or people who worked at some facility that was abusive. Hire an educational counselor, one who is qualified by their professional academic experience and credentials to understand the educational needs and emotional and psychological needs of your child. There are place out there for him!
I agree you need professional advice -- but from a qualified therapist -- not from a program salesman. Ed Cons have no more academic or professional credentials than used car salesmen when it comes to advising parents on educational matters. And they have even less credentials on matters of mental health care.
You seem to understand that the place where your son is now isn't helping him with his mental health issues. At best, he is getting some amount of education. At best, he is not being abused and is "only" suffering the psychological trauma that comes with any sort of institutionalization and loss of freedom of choice.
Is he in immediate danger of harming himself or others? If so, there are hospitals that will keep patients for short periods of time, usually 30 days or less, to stabilize them before sending them home and to outpatient treatment.
If he is not in immediate danger, why is he living in an institution? Are there no psychologists or psychiatrists in your area who can treat his mental health issues? Wouldn't that be better than "benign negligence?" Are there no other school options (online school, for example) besides the public school that was abusive? If not, then maybe he's not in a position to deal with any sort of school right now. Is there some reason he is not being encouraged or even allowed to grow up, make decisions (yes, even make mistakes) and take on some personal responsibility?
You've stuck him in a sort of limbo, where he's 17 going on 12. The sooner you let him stand on his own two feet and figure things out for himself, the sooner he will start moving toward adulthood.