I think you underestimate how brainwashed they are.
I’m not sure all the brainwasing in the world can overcome the power of someone subjected to a lifetime of starvation suddenly being exposed to things like apples, bananas and Hershey bars.
I’m not saying that the Norks will flip sides, but rather that there’ll be a massive breakdown in unit cohesion that will effectively halt the advance and allow the invasion to be contained.