I waded my way though the dungeon, killed the queen, killed the rest of her minions, was merrily looting the eggs when the dungeon puked me out (without the queen being chopped up, left in her domain..).
As far as I knew, unless I exited the dungeon, it shouldn't be destroyed, no? Or was it on a timer?
Wiki says: "After all hearthlings have exited, the dungeon will continue to visibly shake for a few minutes, then collapse into the ground, never to be seen again."