“What would it take happening to Russia to make it withdraw offensive forces and be preoccupied elsewhere instead?”
My own preference? That Putin dies (by whatever cause) and his replacement puts an immediate end to the war.
While I think this is likely it is also shaping up that China is seeing Russia’s weakness and is starting to look at recapturing Siberia from Russia.
Unlike an attack on Taiwan there would be no repercussions from the West if China invested the effort to seize territory that used to be theirs anyway.
In the event of such an invasion by China the Russians would have no choice but to end the war in Ukraine and fight the Chinese or else abandon Siberia to the Chinese.
Either way, Russia would be skunked.
—> and his replacement puts an immediate end to the war.
Russian elections are May (I think I read).
Behind Putin, fighting to replace him are hardliners who want all out war.
I'm sure the CIA would approve. Just one problem Russia has many choices and if China invaded Russia (their ally) Russia in its depleted current state would be forced into a corner.
The only way out would be to use nukes on the invading hoards. Since almost no one lives in the area Putin would not hesitate and he would have moral authority to use them since Russia was being invaded once again.
The Russian bear may be wounded but it's still very dangerous. The Chinese are not stupid.
Far, far more likely, Putin's Replacement will put an immediate end to Ukraine.
...China is seeing Russia’s weakness and is starting to look at recapturing Siberia from Russia.
China will reevaluate Siberia's administration the day after The Second American Civil War is settled with the permanent division of what used to be The United States Of America, and not until then.
Of course there would be no repercussions from the West no matter what China did anywhere in the world.
Be careful what you wish for, you may get it in a way you don't want.