Voss will arrange a meeting between Forsaken civil representatives and Calia, Derek and Faol. Calia will be accepted as the new queen on the condition that she will share power with a new Desolate Council, of which Derek, Faol and Voss will be members.
Calia will serve as a bridge between the Alliance and the Horde going forward.
Remember Uther's Tomb update for no apparent reason? It will feature in the unlock scenario for the new Allied Race, and will be the starting location for newly created lightbound undead. Uther's spirit will be involved in the process, but it'll likely be like was implies in the Lightforged Draenei scenario: the transformation carries risks, and can only be completed succesully by those with strong enough conviction, so not all Forsaken will readily take this "cure".
Tirisifal and Lordaeron Capital are blighted, but a rebuilt Andorhal in a revamped Western Plaguelands would do the trick as a new home, again with a bridge to the Alliance Lordaeron survivors, and Uther's Tomb is right south of it.