Confirmed by Ion in a recent Chinese interview.
Q2. Will Calia Menethil and Derek Proudmoore join the Horde in the upcoming story?
A: This is a complicated issue. Calia is very sympathetic towards the situation and condition of the Forsaken, but she will not join the Horde because of this. Additionally, the number of Forsaken who may welcome their presence is not fixed.
We have been spared from a great evil.
So that means she will lead the undead night elves… back into the alliance right?
A positive revelation, to be sure, but that still leaves the Forsaken as a leaderless faction.
Calia or not, without Sylvanas the Forsaken aren’t really at all what I loved since Vanilla.
This news is just a cold comfort.
It’s not so bad once you get used to it. 
Lightforged Undead Ally race incoming.
Maybe she will join the Horde because of something else 
And now I picture a scenario where Voss’s plans to get Calia as the Forsaken leader failing but Calia encouraging Voss to lead them.
Im not sure how much of a lore guy Ion is to be taking his word. It also doesn’t stop Blizzard from changing their mind down the line. What else would Calia do?
Become a Khadgar. Neutral questgiver. Lead players around on quests centered around dying and the Light.
Helcular the Lich for Forsaken leader.
Sylvanas will most likely come back after her redemption.
He’ll need a title comparable to the Banshee Queen.
It’s more than likely Voss if not Calia.
Voss says that she will speak for her people, but not lead them. She says that, she has someone in mind already.
But wasn’t that supposed to be Calia?
Unlikely, imo. The most “redemptive” outlook for Sylvanas that I can see is something like becoming the new Jailer - assuming a position of power that keeps her “important” in an abstract sense but removes her from the story at hand.
If something like that were to happen, Nathanos might come back, though.
One can only hope.
She never should have left in the first place.
true, she should have never left her supposed grave
I breathe a sigh of relief, but still curse Calia for existing in the first place.
I’m hoping that this either means she outright refuses Voss’s offer or tries and immediately realizes she dun goofed and leaves.
So I guess… Voss is the Forsaken rep?
I miss Nate.