I think this is probably how the Chinese intervention, if they choose to intervene, would start, to restore the current DPRK/ROK border after a ROK/US incursion into the North. It seems likely that if that happens, DPRK would escalate with nukes in order to force China's hand into full intervention on their behalf, as USA's current doctrine, to the best of unclass knowledge, is to respond in kind to nuclear aggression. Once that happens all bets are off, unfortunately. I don't see how it ends well for anyone once China decides to get involved, given the current doctrines and state of military technology.