I'm not sure what the standard of living for the masses in the North is, but if reports are accurate, I think "stable" and "subsistence level" are probably interchangeable. Ever notice that you almost never see photos of regular N Koreans? Mainly you only see their relatively better-fed military. Best case scenario was (a long time ago) to have done our damndest to pry open the hermetically sealed information dome that the regime places over their people and give them a little sunlight and vision of what the rest of the world lives like. Either that ship sailed, or it is completely impossible to inform people on a basic level what their lives are live vs. what their lives should be like.
I doubt the South could handle unification without major aid. I think China would have a really hard time dealing with a collapsed North, too. I think the silver lining in this recent conflict is the fact that what to do with the North can't be solved without China's involvement without millions losing their lives -- and that's what will drive everyone to tamp down the flames. I can't believe I'm saying it, but too bad the UN sucks so badly. Some effective overarching institution could actually be helpful.
Edit:
Either all that drivel, OR
China is actually driving all this conflict and can shut it down when the see fit. Their motivation is to get the West to keep the economic stability and to make sure they're not labeled "currency manipulators".