Obviously. The Chinese and Russians wouldn't engage in direct combat with the US in this day and age, though. Proxy war or no proxy war.
They would of course provide material support for any resistance, assuming there would be one. However, I suspect the North Korean populace's forced reverence for Kim Jong-Un isn't exactly on the same level as say, the Mujahideen's religious fervor.
>But yeah, for sure this time the Russians and Chinese won't bother.
Is that sarcasm? I genuinely can't tell. Direct conflict with the US is a terrible idea, and both countries know that.