The mapgen tiles in Gravitas lobby can be damaged by comets, but they aren't properly destroyed. Instead, they lose their solid component, start letting gases, liquids and comets through, and stop counting as tiles for dupe pathfinding. Pressure damage may sometimes do the same thing.
Loading a save resets them back to undamaged.
Steps to Reproduce
Watch comets damage Gravitas lobby. Notice it starts leaking gas after a while. Track the leak - at least one tile will exist but not block gas.
This issue has not been confirmed by a developer yet.