No old god is dead, they just return to the void.
But, Wrathion has a piece of N'Zoth in crystal in the heart chamber. Then there's the Xala'tath (Blade) angle. .. Then there's the Xala'tath (Person) angle.
Given's Blizz penchant for cashing in on nostalgia, I expect that one day we will see "the void expansion" where each of the old gods we know comes back in some fashion. If it goes that way, I'm hoping they get a patch/tier each, and not just 3 side bosses in some new big bad's dungeon.