Sure, but Vietnam or Korea starting a suicidal conflict with China is equally unlikely. And nobody would have expected Ukraine to behave so foolishly to get into a conflict with Russia. So a war against a pro West Russia should be a valid scenario. China should have some plans for every potential war, no matter how unlikely
the difference is that Russians will never have overt US support even if they join the EU - they'll have the power to pull the EU away from the US instead to form their own "alternative west" focused on the German-Russian-French axis.
However, I hate to say this, but Asian white/west worship is a well known and historically documented phenomena where Asians will fight and die for the US ferociously against other Asians (and only other Asians) while cowering against westerners no matter what the atrocities they commit, both at home and abroad. Even NATO countries don't do that.
Example:
1. millions of South Koreans were killed by the US and the US sponsored military dictatorship. South Korea is one of the most pro US countries in the world with 84% approval rate.
2. millions of Vietnamese were killed by the US and the US sponsored military dictatorship. Unlike South Korea, the Vietnamese military dictatorship was defeated. Nonetheless the US has a 78% approval rate.
3. Philippines was colonized by the US for 50+ years after a war where Filipinos were put in cages in human zoos. The Philippines has a 94% approval rate of the US.
these approval rates far exceed the approval rates of the US in core NATO and treaty allies including UK, Canada, Australia, Israel, Germany, etc.
So if you told me that Russia would fight and die for the US against China, I won't believe you. I wouldn't even really believe NATO would fight and die for the US against China - they'll use the North Atlantic Charter as an excuse because they don't want to die for nothing. But if you told me that South Koreans and Vietnamese would do it, especially if they had overt US support, I wouldn't dismiss it at all.