China will be protecting their borders against North Korean refugees. Germany is the lesson for why Korea will not be unified. South Korea can't carry the financial burden of absorbing the millions of backwards, starving, brainwashed North Koreans.
I think the ideal outcome for everyone involved will be regime change following by a slow-paced transition of North Korean's populace into the civilized world
If the norks start losing badly, China will enter to create a buffer zone, at the very least. The best solution is to give the mainland part of NK to China and the Penninsula part to SK. The two can share the burden and we end up with one Korea.