When and if China ends our power in the Far East they will turn on the Russians and there will be a nuclear exchange between the two thug nations.
I think China believes, probably correctly, that all they have to do is wait out Russia’s shrinking population for a while, and then when the time is right just start pushing here and there on the border, as they often do with India. They’ll just use their vast numbers to probe and prod at first, and then eventually invade a weakened Russia. At that point, Russia could be so weak that they just acquiesce to a gradual, non-violent colonization of some of their territory, rather than risk war with a huge adversarial army.
That is the one thing I know will NEVER happen. Never Ever.