Nerubians

The first raid for World of Warcraft: The War Within will be the Nerub-ar Palace, located at the back of the City of Threads in the lower levels of the Azj-Kahet zone.

This one’s never going to be solved, because we know that Doomguards were created by the Titans to hunt down those that engaged in sacrificial magics, implying that there were Warlocks before the fall of Sargeras. We know that the most famous Warlocks, Archimonde and Kil’jaeden, were Mages on Argus before Sargeras came and converted to Warlock magic as a result, and that the modern Warlock tradition derives from their teachings, so even former Orc Shamans who became Warlocks learned from Kil’jaeden’s teaching of Gul’dan and thus learned from a former Mage.

In the end, all we can do is go on with The Queue.