I presume hes okay. He checked in voluntarily which is a good sign, he hadn't been getting really drunk for years and being a total alcholic so I think it was relatively minor. As I see it, he checked himself in and he wouldn't leave until he feels as if he is ready. But then again, can't say for sure.
i think what Xander meant was that Nick hadn't gotten to the stage where he needed to drink everyday. he recognized that he had a problem and checked himself in to rehab before it got any worse. which i also think is a good sign.You don't enter rehab for "minor" alcoholism.