This isn't a big deal. He basically has two options. When you fully dislocate your shoulder, you tear the ligaments that help to hold the ball of your shoulder in it's socket. So, his options are:
1 - Put it back in, do some PT to strengthen the muscles, and then play. He will be sore for about a week. The upside to this, is he can play before the end of the year. The downside is now that those ligaments are torn, he will continue to dislocate/subluxate his shoulder throughout his life, need a couple of days to feel better, repeat.
2 - Have surgery to repair the ligaments. If he does this he will be out 6 weeks as it heals, ending his season. BUT, the chances of subluxation/dislocation again are about 5%. If I were him and the Jazz, this is what I would do. This season is shot, I say do the surgery.