I don't know, but I don't like it. Whatever took him out is more powerful than anything I've ever seen - even I'd be reluctant to take it on alone.
Two theories: Either he was completely annihilated by whatever this was. Or he's somehow disappeared.
I just hope the portals are not involved. It seems like an eery coincidence, right?
The other question I have is if he's still around, how come he hasn't gone after the stones yet? According to everyone's timeline, he should have attacked Xandar by now.