PLA is considering the deployment of peacekeepers in the DPRK
Yes. They are ready to use some 150.000. troops (they are very close to DPRK boarder).
They will not tell it directly, what they does.
I have no idea under what sauce People's Liberation Army of China will enter to DPRK, but it might happend very close.
Americans can destroy the missile strike all launchers in North Korea and the Chinese army immediately conduct a ground operation on clearing of North Korea from the dictatorial regime of Kim Jong-UN