When a thick ceiling has no support, the entity known as Collapsed rocks appears to act as a supporting pillar. If a colonist completely mines out a mountain but ends up getting crushed by Collapsed rocks, they seem to be completely erased out of existence. None of the other colonists remember them and they don't even suffer from negative mood effects.
And a sidenote, I feel like sold animals have too high of a probability of just randomly appearing back into the map.
And a sidenote, I feel like sold animals have too high of a probability of just randomly appearing back into the map.