so, with the destruction of undercity, by sylvanas' own hands, it isn't just the city being destroyed, but all of tirisfal glades being lost to the forsaken.
We know that the forsaken were being evacuated to orgrimmar though portals, as we saw then getting back to orgrimmar after the scenario. I think its more then fair to say with undercity lost, and blizzard setting up this strong theme of the alliance claiming eastern kingdoms and horde claiming kalimdor, that there will be no forsaken towns left with the city lost, and the alliance forces claiming the land like silverpine and hillsbrad.
Now though, its time we faced the facts of what this does to the forsaken as a people. I can remember back then undercity was originally taken over by putress and varimathras, then the forsaken were brought to durotar for a save haven for them away from the fighting happening in the city. I can remember back then, forsaken citizens would say how much the durotar heat was cooking them, and it made sense, there undead walking people, they lived in a dark, sunless place whos city was set deep underground, so it be cold and dark, something you would expect a walking corpse to have more comfort in. The heat from places like durotar would be a strain on them to survive in.
So now, the forsaken have lost their land, but they also lost there place in the world there they could easily survive and not be in a stare of suffering more then they already are.
Thinking about it, there isn't much going for the forsaken right now, kalimdor is a continent with some extreme weathers from deserts to freezing cold mountain tops. At this point the only place they might find refuge from the heat would be ashenvale, since the night elves will no longer have a place to get reinforcements from teldrassil.
But that in itself is a problem, since all these years, orgrimmar have wanted to claim ashenvale for its lumber and resources, and without the night elves around to protect it, they would now do so. So even then, its unlikely the forsaken would be able to claim it.
I wouldn't imagine desolace working either due to the heat there.
The only place i imagine would probably be fel wood, since the trees are rotten there.
But, I'm saying all this, what I really believes going to happen is the forsaken are never going to be relocated to somewhere, and blizzard will just move on with whatever comes next before establishing the forsaken having a new home.