Ustoo, you are doing not only the right thing but also the most loving thing you could do for your son right now...letting him live the consequences of his actions.
If he is released, perhaps have a list handy of detoxes, shelters (that all have counselling and will help him get in a program if he wants one), and perhaps the local AA or NA number where he can call people who can help him more than you or I ever could. That way he has choices, good choices, and you don't have to be his only choice. Then let him make his choice and live with it.
My prayers go out for all of you. My thoughts are that his Higher Power has him exactly where he needs to be right now,
Hugs