Some fic ideas I've had, starting with nations:
Do Norway, Sweden, and Finland still exist in Y90? There would still be Norwegian, Swedish, and Finnish speakers, but there would be no one left who really remembered what it was like to live in a unified nation of millions of inhabitants; most would know only their own fortified villages, or those close enough to reach by short sea voyages, though there would still be some older people (like Trond) who heard about nations from parents or grandparents. With no remote communication technology and all travel being dangerous, I think nations might well fall apart.
...
Anyway, I can imagine stories about people in some of these smaller communities: maybe they're even now just being brought back into contact.
Maybe there are people trying to hold the nations together, and meeting either active or passive resistance.
Might there be judges "riding the circuit" to the small towns? (This used to be the case in America.) How much authority do people grant them, and why?
Has Christianity really disappeared everywhere, or are some of those little villages Christian communities or communities of other faiths?
Those are all interesting questions. (and I cropped the quote just to make it "lighter").
IIRC, and staying with the canon, radio communications still work, albeit with varying levels of quality and range. However, do small villages have radio equipment? Some may have, others not.
I believe the connection between the smaller settlements and their Nations would be quite loose, probably like it happened in the Middle Ages, when local leadership dealt with almost every issue. The presence of the State was felt mostly through taxes, overall laws and decrees and, of course, the military.
That's a lot of fOoD for stories here.
I imagine a small group going from settlement to settlement. That band of travellers could include a judge (like you mentioned), a doctor, a mage, one or two craftsman and a small escort, perhaps four or five fighters. They would collect and deliver mail, valuable supplies that cannot be produced localy, medicines... and help with local issues the village couldn't solve by itself, be it a sick person, a dispute that can escalate into a bloody fight or a particularly annoying troll.
They would also escort people between those places and larger towns (a young person that's going to be trained as a mage, an older person returning to the village after training, a magician that risks life to earn some money...). Ah, the stories those travels could fuel! I feel tempted to do one right now!