> secession, you cannot secede in NK, even individually. They have machinegunners at the border, shooting everybody trying to run away

That's not what secession means.

Sometimes in authoritarian regimes, a portion of the territory under controls realizes it is powerful enough to be its own master. The ensuing conflicts might then topple the whole thing. That's how the Ottoman Empire fell for example.

Disintegration is always a risk for large entity.