Yeah, he died and ended up as a ghost. But apparently Doctor Sleep is about ghosts...too? I haven't read the book, but according to the trailers -- Danny revisits the Overlook Hotel.

Of course if he ended up as a ghost, how can Jack appear in it -- he's older than that? Although I guess he could voice it. But so can a lot of people -- there's a lot of people who can do Nicholson impressions.