Ugh, a dislocation. Sounds like he's had several. From experience, I can say that when the shoulder pops out and goes right back in, it's not so bad. Usually you're sore for a few hours, maybe a day. The more it comes out, the more the long-term pain goes away (because your connective tissue isn't tearing as much). However, when the shoulder doesn't pop back in, that's when the real pain and structural damage occurs.
Hopefully he gets surgery on it early this off-season. It's a quick surgery that can be done arthroscopically, and the recovery time is only about 6 weeks. I went from dislocating my shoulder about 2 to 3 times per month, to only have one very minor separation in the last 4 years.
It wouldn't shock me if he's able to play in Game 4, but I could also seeing him being out a week or so.