In the end, China is in economic trouble, and really can't spare the resources to try and help North Korea at the moment. North Korea is getting on the nerves of even the most against America countries, I can't see North Korea with more restrictions, fake weaponry (Certainly didn't have much earlier) and South Korea would immediately be taken back by the US before North Korea had time to set up shop.
North Korea only really has China to back them, and South Korea has the United States Military backing them, so it really becomes "what would happen if the US and China went to war, with some relatively insignificant extra factors." A conflict like this would be nuclear annihilation, but the US, would overall win because the US has the largest military spending in the world.
North Korea has Chemicals, Bio Wepaons, Nukes, and drones.
Also, North Korea Has Less restrictions then South korea.
China and russia are more cooperative then America.
Russia and China also are closer to north korea then america.
South korea is too heaistant and Skepticalnto ask help.From Japan.
And South koreans Don't exeoect an invasion.