How long is he expected to stay at this rehab? The longer the stay, the better his chances for recovery. Experts say that 90 days is minimum requirement for effectiveness and 6 months to a year is better. Rehab is not magic, that's for sure. If he comes out and is seriously working his program (going to AA meetings, calling his sponsor, doing step work etc.) you will know he has a fighting chance. If he comes out of rehab and reclaims his spot on the couch, then his actions tell you he's not done.
If you can, get to Al-Anon.
Read Co-Dependent No More (Beatty) and Why Does He Do That? (Bancroft) as soon as possible.