Outside of theorizing who the next big bad is supposed to be, I think a genuine question needs to be asked about how, after all of this, any of the characters (including our own) cannot be forever impacted by what has happened.
We’ve seen the afterlife. There can be no religion or belief on Azeroth that is not impacted by these events. It’s no longer a question of where we go when we die or how our gods work.
There is apparently a universal concept of sin, and therefore right and wrong. Why do the Alliance and Horde matter when we’re starting to unravel the mysteries of reality itself? What petty political squabble can have any importance or meaning when we converse with gods?
What could the next big bad threaten us with that is worse than Hell or annihilation of the soul? Unmaking of reality loses its sting when everyone threatens it. They are all slightly different flavors of the same thing in the end. Just another day on Azeroth when an otherworldly entity shows up and threatens to undo reality at this point.
I’m not sure how Blizzard gets itself out of the corner it has painted itself in this time.