Skoll Shorties

Plus Teldrassil being actually destroyed is a permanent loss, whereas you can actually cleanse the Blight from a place, and I wouldn't be surprised to see that happen at some point either in WoW or Warcraft 4. Teldrassil is gone forever though.

Teldrassil is being completely destroyed. Undercity is probably getting updated because they already just updated the outside of the battle for lordaeron event and only spread plague everywhere.

Level 1-110s will see Teldrassil and Undercity as they were but once you do the quest they'll be gone. Both can be changed back by the Bronze Dragonflight though.