This is where FFT (see thread elsewhere here) or MST (multisystemic family therapy) would be an excellent choice.
Arresting the child is an insane idea-- with the drug laws here, he could be sent to jail for decades. With a record, his odds of recovery are dramatically reduced. Plus, the violence etc. of jail can produce increased drug use later.
Wilderness is no more likely to solve the problem than a re-run of psychiatric or addiction care is-- the older he gets, the more likely he is to change, and people will often "credit" the last thing tried with the success when what really happened is that he aged out.
Wilderness also has the problem of being poorly regulated and potentially harmful.
However, a practical suggestion re: the dealing. he's gotta keep the stash somewhere. if you ensure that that is not your house, you will crimp that style.
also, if he is endangering your younger kids, you have every right to protect them by expelling him from your home, whether to treatment or elsewhere.
patience and persistence is called for here-- and if you still feel you must resort to wilderness, ensure that you choose a program that allows maximum contact with the child, has the highest number of licensed professionals, doesn't shill for extended treatment in a "therapeutic" school afterwards (you'd be amazed at how many are aimed at recruiting into longer stuff), doesn't focus on "tough love," allows decent equipment and has a great reputation.
That said, there have been deaths in the programs with the best reputations and these deaths have been caused by assuming that kids' medical problems are 'fake' or 'manipulating.'
see helpatanycost.com for additional info.