He didn't kill them, he just thinned them out to the point where they couldn't challenge him. Now that he is gone, I am sure someone will absorb a lot of his forces and start to gain power again.
Of course, I don't think he's gone, but his power is probably VERY much so limited now. I imagine he's just like a ghost now...an Ascended being that cannot take physical form or in any way directly effect the physical realm. But he can manipulate people. Think Sauron from LOTR.