So I don't really* think that the long months of summer could ever produce enough food to keep settlements going through the long years of winter.
In Myperborea, I kind of try to keep the Howardian civilization-vs.-savagery thing going, though mostly under the surface. It's kind of a PC vs. NPC thing. Like for example there are PC druids, who embrace the balance &c. &c. but REALLY are accessing power through a certain progression that gets them more power up to potentially ridiculous levels -- if they can stay alive. Then there are "chaos" druids (specific references would include "Ruined Palace of the Metegorgos" and some stuff from Arnold K's blog) that have given themselves over fully to natural forces and are, at best, orthogonal to humanity now. The zooanthropes from the Gene Wolfe torturer books are also analogs here.
But then and but so the point is that then there are the "civilized" classes, and these are the people that make human civilization possible pretty much everywhere except maybe the Khromarium peninsula. Druids are a solid example again and probably the most common ones. These are the people collecting prisoners and captured monsters and deformed adventurers to burn in the wicker person at the festival days. Their dedication to channeling life energy into the ground creates tiny arable zones that endure in all except the year of full darkness, where all life energies are canceled. But even in spring and summer years, most of Hyperborea is just too damn cold for growing enough to support human settlements.
And so the blood. And so the lotus. And so the people of fell aspect and intense mien who will hire adventurers and use them for whatever they are worth to get whatever is needed to shave the fine percentages between existence and extinction for these isolated settlements in the great dark.
Fun part is me, I don't care whether human civilization survives in Hyperborea! I'm just letting the dice talk!
Anyway, that's my take on winter: blood, magic, death, and determination.
*No math has been done, nor do I care about it. This is gut level. Summer in Hyperborea is still pretty damn cold. And the areas around settlements safe enough to cultivate are going to be pretty limited before UNBALANCED ENCOUNTER TABLES stabilize the population at "inside the damn walls."