Raven Omayn has vanished from the Council Hall in Sadrith Mora, along with the other mouths. Although this is presumably due to the fact that the counselors are dead, I can't be too sure, as I've had similar (albeit resolvable) problems with actors in other cells. I am trying to start the vampire quest for Omayn and am obviously unable to do so--- I'm trying not to leave anything undone in my file. I have searched everywhere for this issue and was astounded to have found nothing. Is there a way I can get her back? If not, what is her console ID?

You can resurrect her. Type in the console:

Resurrect raven omayn

PlaceAtPC-> "raven omayn" 1, 120, 1

To answer your other query, the Mouths disappear when their counsellor dies and that's why none of the mouths are there since you say you killed all the counsellors.