FYI should anything happen China has a defensive pact with North Korea. They’re not reinforcing the border rail lines and didn’t build a new bridge over the Yalu for the sake of tourism.
Pacts come and pacts go. The streams of refugees coming over the Yalu might conceivably have weakened their ties, as well as the brinkmanship with the US. China is trading with the US. That doesn’t mean they suddenly love America, but they have considerably less reason to love NK at this time than they did back in the 1950s, and a war with NK would threaten their never-ending flow of crappy manufactured goods to the US, should they decide to fully honor the letter and spirit of this pact. My guess is that they would do what Asiatics tend to do in these situations, and nominally stick to the bare letter of this pact, while in fact quietly doing all they can to undermine NK.