Regardless of the number of nukes, China's biggest fear is having to deal with the vast number of potential NK refugees.
One thing's for sure: Those refugees won't be heading South....their communist neighbor would be the likely choice.
That's for sure, as the south would have been nuked, it would not be a healthy place to run to and china would attack from the north and west which would leave refugees no place else to go unless they are very good swimmers lol.
But the other scenario is that NK nukes SK and then china nukes NK, this way there would be zero refugees and do not think for a second that they would not do it.
People sleep peaceably in their beds at night only because rough men stand ready to do violence on their behalf - George Orwell