You are severely overestimating the extent to which an economy can be self-sufficient. Technological know-how, required resources, manpower, Russia simply doesn't have enough to weather this bullshit. You can do the self-sufficiency thing with smaller sanctions like Russia was under in the past but the rest of the world went MAXIMUM SANCTIONS from the get-go and it's probably gonna get even worse because the EU is already speedrunning finding alternatives to Russian oil and gas, which means that even Russia's resource exports are gonna take a hit in the near future.
I also don't get your point about China. They are tied into economic globalization more than most others, part of the reason they started cutting Russia loose so quick after the Ukraine invasion started is because they don't wanna get bitch-slapped with similar economic troubles.