Deathwing already caused the Firelands to collapse into Azeroth resulting in Sulfuron Spire showing up there(there are also portions of the Firelands bursting into Darkshore, Ashenvale and Stonetalon Mountains).
If the World Pillar collapsed we’d be seeing parts of Deepholm all over Azeroth just as the Firelands has been doing the same!
Skywall has also collapsed into Azeroth as seen with the pillar of Air bursting out of Westfall and the entrances to the Skywall Dungeon and Raid showing up in the skies of Uldum.
Abyssal Maw and Deepholm currently are the only Elemental Planes that have not collapsed even partly into Azeroth even if Entrances to them have been made in the Ocean Floor!