That monastery would be awesome, and then we could have Russians in the setting too!
Something wild I've been wondering is if there could be tiny bands of nomads wandering the Silent World in distant places. They wouldn't be "communities" so to speak but rather an extended family or three, no more than maybe 20 people per group, all immune, shunning ruins and always on the move, secretive and furtive, maybe meeting up with another band every few years. There could be boat people, living on large rivers and lakes, sleeping on the water or tiny islets by night and foraging by day. Maybe hunter-gatherers on open plains, who burn the grasses every late fall to clear the land, with the most sure-eyed being spotters to alert the rest if there was any danger and they needed to move on. In order to keep quiet their language may have become simply sign language and bird whistles for long distance communication. A couple amongst their clan might be mages of sorts, using whatever innate talent they have to determine if danger is near or to try to keep it from noticing them. Of course they'd probably keep a few cats following them around too. They might have a few metal tools they've been able to cling to but would basically be stone age, but they would still be survivors.
To live, they would've had to become so quiet and hidden that if Our Heroes were to travel to some distant land and wander about, they could be followed by one of these groups for days without even realizing it. They wouldn't know until one night they were camping and all of a sudden people emerge from surroundings without even making a rustle.