So i generated a world where the only human civ got wiped out by elves. I wanted to see how that would affect the sites so i made an elf adventurer to go check it out. Of course i spawned on the opposite side of the map and got torn up by bogeymen attempted to get there (since there are NO actual elf/dwarf sites to speak of). After repeating that a couple more times i went with a demigod dwarf axe-savant. So many bogeyman bisections/decapitations.
Anyways once i did finally get there there were no actual ruins, the hamlets and towns pretty much exactly the same as if there was still a civ, except that 'there is no capital' and the coins are from a period of no rule. I think the local government groups were still intact, but i didn't check. So i did some quests for the family-less spawned-from-midair humans killing loads of night creature spouses. Turns out that once you've done a certain number of quests for a given town/hamlet they'll stop giving you quests by responding "Isn't that enough?" when you ask if you can be of service. I think it's because they have no capital/civ leader to redirect you to for further quests.
So after dinking around killing things and buying/selling all sorts of stuff, i decided to go get more quests from the nearby fortresses. So i show up at a fortress and notice odd behaviour in the inhabitants. Firstly, all the warriors are wrestlers and have no clothes. Secondly, they're all hostile to me. I then proceed to get kicked in the head and die from a mild concussion.
So civ-less hamlets/towns still spawn friendly villagers and fortresses spawn hostile wrestlers. I think it might have something to do with fortresses not being attached to local governments. I suppose they could be a good unlimited source of weapons training if you have steel armor and make sure not to get swarmed. I'm gonna have to try and gen a similar situation again to see if the fortresses still spawn lords (i compulsively delete worlds when i'm done with them...Oops.).