The most realistic, and highest success chance scenario is that North Korea will coordinate attack with China.
In all conceivable scenarios, NATO will have more resources even after 100% one sided nuclear attack on it (3000-4000 warheads,) and be able to subdue both China, and NK with conventional forces, and standing armies alone.
Not to say, China's neighbours will not stand still too.
Even a whatever pyrrhic victory will likely be the end of political regimes in both NK, and China.
If they will attack, they will weight in that price first.