The new old war in Korea

[Crusader]

What I wonder is whether any nation would retailliate with nukes against NK, should NK use a nuke on SK or it's allies. Sure, on the scale of power NK's nukes are puny, especially when put against modern nukes which can reach almost 1000x their power. (NK's nukes are in the kT range, but the USA and Russia have bombs in the MT range and then pretty much decided to call it quits, since making an even more powerful bomb is almost pointless and even dangerous for themselves, even if they throw it at the other side of the world).

What I think is that should NK throw a bomb anywhere, China would either sit back and watch NK get massacred with conventional arms or invade it themselves to make it a new province of China.

I can imagine a scenario comparable to the 2008 Georgia-Russian war. NK starts it, SK retalliates, The world is staring open mouthed in the opening moves of the war and starts deciding on what to to do and during that, China immediately makes it's move and invades and takes over NK. This nets China a new province and prevents nuclear retalliation against NK. China doesn't want nukes falling on NK because the nuclear fallout is likely to spill over China. It's like indirectly throwing a nuke on China. They wouldn't have the crater(s) but the radiation would fall over them with all the terrible long-term consequences.