However, I don't think China would want NK to actually use the nukes. China would want to maintain status quo.
So, if it looks like NK is serious about using nukes, China (I believe) will allow a U.S.-led invasion. But, as you said, they wouldn't want the U.S. to get too close to their border, so maybe China itself would invade from the North, creating a buffer zone between itself and the U.S. forces.
Another scenario: Maybe in the case of a U.S. invasion, China will allow the Kim dynasty to enter China and request asylum, and in return China will occupy a small part of North Korea to keep as a buffer.
I don't know as much about the Korean conflict as much as some other members here, and many of my guesses might be wrong.
However, I don't think China would want NK to actually use the nukes. China would want to maintain status quo.
So, if it looks like NK is serious about using nukes, China (I believe) will allow a U.S.-led invasion. But, as you said, they wouldn't want the U.S. to get too close to their border, so maybe China itself would invade from the North, creating a buffer zone between itself and the U.S. forces.
Another scenario: Maybe in the case of a U.S. invasion, China will allow the Kim dynasty to enter China and request asylum, and in return China will occupy a small part of North Korea to keep as a buffer.
I don't know as much about the Korean conflict as much as some other members here, and many of my guesses might be wrong.