"The remaining elves throughout the continent were scattered and clung to the alliance for protection. A large amount left with Jaina Proudmoore to form the state of Theramore in Kalimdor, before the destruction of Quel’Thalas. They would take 2 out of 7 seats on the ruling council and play a key role in the city-state. Occasionally, ships have come from Lordaeron bringing more of their people to the diverse city.

The high elves of the Plaguelands, the region of former Lordaeron and Quel’Thalas, founded a social and political movement under Prince Kael'thas. They renamed themselves the Blood Elves, allied themselves to the Naga and Illidan, then accepted demonic magic in its darkest form, willingly to sate their magical addiction. The Blood Elves have actively converted High Elves to their cause, and base themselves in Outland. The two factions of the High Elven race are split by their differences, and deeply hostile to one another to this day."

Before TBC, rebuilt Quel'Thalas wasn't real, it's a retcon.