Nothing in story we know suggest if there will be 1 or 2 more chapters - we still have 3 big unused cards: Anduin as boss, Arthas (most likely ally, not boss) and Jailer. From hinted places we have Sepulcher, Gardens of Life, afterlive for inventors (don't remember name, but it sounded like Mechagon 2.0 hint), more SL realms in general (doesn't Blizz straight up said we will see more? it's not that relevant anyway, since it was way before release and plans could be different, but I think it was said).
I'm not sure Anduin will be in his Death Knight state for much longerm possibly by the end of 9.1. No damn idea about Arthas but I do wonder if he's in that place where those Soulshards of Uther and Sylvanas are(Is Arthas's Dad there to?). How the Dread Lords will fit into this I don't know. There's a lot to deal with in the coming year or so.