Actually, according to the books and game, the mana bomb is worse than fel corruption. Fel corruption affects the natural state of the area it affects. The manabomb affects the planar, temporal, magical, -and- natural state of the area. In theory, if they created a patch that opened up Warlord of Draenor's alternate-reality version of Azeroth, there's a giant crater that just randomly appeared one day in Dustwallow Marsh that no one there knows how it happened.
The mana bomb erased all life and magic from all alternate history versions of Theramore that have or ever will exist. That's why the bronze dragonflight (aside from the obvious 'losing our aspect powers') couldn't prevent Theramore's destruction even if they were allowed to by their own laws. It's destroyed in every timeline from that single bomb. Nowhere to go to salvage anything to bring back. Even in timelines where Theramore was never founded.