I'm so very sorry about your son and the entire situation is just horrible. Only you can decide how to handle your wife given her medical history, but I always felt honesty was the best policy.
As far as when or if to allow your son back into your home, well, again, that's up to you. If he wants to be a part of your life, then he knows what he has to do. He's not a child. Why put a time limit on it? He might be 100x worse in 3 months or he might be back in rehab. But, I would tell him he's not allowed in the house - period. If he's going to steal medication from your wife, what else will he steal?
Good luck and big hugs...