World of Warcraft PvP Guides - Blood Elves in Cataclysm Guides
Lor’themar and the remaining Blood Elves move into the forest and purge the forests of the Undead threat, proving themselves to the Forsaken who assist them in joining the Horde. As I said earlier, Sylvanas was the commander of the Ranger General and was good friends with Lor’themar. So with Thrall’s political savvy and Sylvanas’ suggestion, they gain strong allies who help them defend their land.
That leaves us with Cataclysm, which will be bringing the old world back up to modern times. Garrosh will be taking over and he’s probably not going to have a high opinion of the prissy Elves. Not to mention that the Blood Elves and Forsaken are thick as thieves and the Horde has a really bad opinion of the Forsaken right now. Their main plot line, Kil'jaeden, was resolved in The Burning Crusade, while their involvement with Dalaran and the cold war they have with remaining High Elves pretty much goes nowhere.
What if the Blood Elves remained with the Alliance? I personally feel that in Cataclysm the Alliance would have purged the Undercity of the undead and reclaimed their lands in the name of the Alliance. Silvermoon is a great assault point against the Undercity which is separated from the main Horde armies and is pretty much in the gutter as far as Horde relations go.