Well, if there were a thread for fic ideas, I would mention something I just learned off the Nebula site. It seems that Finland has shelters for the entire population in case of nuclear war, which I find awesome in reality. But in the SSSS context, I expect that few people would take to those shelters or if they did, they would probably have food and water for only a few weeks, and then they'd have to come out and face the monsters.
But some people might retreat to a shelter with food and water for years, or at least with enough weapons and ammo that they're able to survive for a long time. Their descendants might still be there, hunting grosslings by day and hiding out by night, not even knowing that other people have survived.
Alternatively, how many trolls found their way into such well-protected shelters, and would have to be laboriously dug out if you wanted to cleanse an area?