I find it hard to imagine what that transition must have been like. Were people traumatised by the sudden collapse of their world or did they relapse into tribal ways the way one might slip into a stinky old dressing-gown at the end of the day? Did anyone struggle to maintain standards of governance and civilisation? The evidence suggests not.
I've read fiction about the last days of Empire and fiction about the so-called Dark Ages, but I've never read fiction that deals with the generation of the collapse- the people who lived in towns one year and in ruins the next. Does anyone know of any?