I've seemingly beaten Molag Bal, and the Ayleid King is taking a little nappy nap now. I just finished The Final Assault, talked to Meridia, yada yada yada... and then there's just nothingness. You walk back into the Hollowed City like nothing has happened.
There's no other main quest at this point. I've heard you go to do the other zone's quests as VR. I'm only level 49 though, so do I have to get 50 then come back to begin VR content?