Thats ASB. No questions asked impossible. Overtime those states are going to modernise and become more "civilized" by your definition. It was already happening when Rome conquered Gaul and the process of state development won't just go away.
Even with something like the Dark Ages, which was . . . disruptive, things were rebuilt to and then past the point late Gaul - heck, Italy in the same period - could dream of.
And "the Dark Ages last longer" would require northerners (from the Mediterranean perspective) being frickin' idiots or savages of the deliberately eschewing "civilization" sort - and you only find those in some fantasy settings.
I'm not saying you couldn't have individual areas be more disrupted, but the forces pushing for rebuilding and improving from "level with" are immensely strong.
Defining, for those concerned, the Dark Ages as 500-8/900 AD - the period before the High Middle Ages and overlapping with Late Antiquity.
"The period the 'barbarian' kingdoms were being built and tested by the forces at work." We can argue all day on how dark it was, but the point is that only if you continue that period of 'state' building resting on such precarious foundations as an individual king's charisma - not even tradition, just his personal presence - are you anywhere near shaken up enough to not move on.