Also, Vivec stated he cannot sense them
He also said that he didn't murder Nerevar.
They became the [censored] skin of the Numidum
That's just one theory. We don't know whether that's true. And we don't know who is responsible for it, although there's less speculation about that. If Azura was responsible, then she might be able to make them come back. The Dwemer couldn't be gone completely, as there are still Dwemer ghosts.
It doesn't really matter what happened to them, as, if they came back, the Dunmer would massacre them.