So what ? They left the camp like that ? I'm supossing the one that bring them to the camp will comeback eventually because she the only one with a face drawn. Well if the last earthquake didn't wipe the camp. Btw, no wanted to say it's unrealistic but if an asteroid was powerful enough to wipe out all the center of Japan, I can assure you it will have cause more naturals disasters and mosy likely a climate change, well the climate change did happen at least. Although it was already unrealistic that the asteroid will fall on Earth in the first place without being spotted first.
In all of that, i'd say that Kunohama's behavior is more understandable, she is still terrified by what happen when she was a kid so now she found someone she like, she don't want to history to repear itself. If her behavior isn't exactly correct, i understand why she is like that toward Nagi.