I have been through something like this myself and seen it often in treatment centres.
Stage one - bewildered, frightened, open to treatment.
Stage two - Group dynamic kicks in, get comfortable, know "the form", dodge the issues, gain validation from like minded inmates. Cousellors try to break through.
Stage three - Imminent departure, realise I have done nothing about myself, have no plan to survive out there, fear sets in again, ask to stay longer.
Stage four - had to leave, drank again, Go back to stage one, do not collect $200.00
Perhaps other issues are indicated here but his medical specialist should be on to this.
Rehab can be a great way to get started, if one can stay open minded and make the most of what is offered, but it must be followed up with solid support and effort towards a new way of life. Otherwise nothing permanent can be accomnplished.