Any breakup of Russia into a number of smaller yet all nuclear armed states would likely appear as a worse scenario to all outsiders, probably the same applies to the idea of a perpetually Rogue Russia. Whereas the way to end the war from within is fairly simply = Putin out. The more likely scenario is that the elite enabling Putin would safe their beans with some change at the top, forced if needed, at the end of the day it wouldn't be too hard to pass this whole war off as "Putin's Idea", "Putins fault" and while that might not change much to Russias leadership, for the west this would likely suffice (from a stoic and pragmatic pov) if it also comes with a withdrawel of the Russian army from Ukraine and some further settlements trough peace negotiations. It's rather that it would be expected that for the Russian leadership it would be easiest to sell a defeat in Ukraine domesticly "as long as they can all blame it on Putin", while still being able to retain their own interrests.
I'm pretty sure btw that China, although having expressed some support to Russia, also made a threat to Russia so to refrain from using nukes in an offensive fashion. It never benifits an outside nuclear power to see the potential of a global nuclear exchange increase for a matter that is not of their national interrest. One of the best example's of such restraint to Nuclear warfare is imho Brittains war with Argentina over the falklands, as it is really the only scenario in which a non nuclear power dared declaring war on a Nuclear power. Afaik, the USA did support the Uk to some extend, though on the understanding that no nukes would be used, the more so because it appeared as a "geographicly limited conflict, with limited stakes". Why did the Uk not threaten to nuke Beunos Aires, starting off by vaporizing some smaller Argentinian town or some army base as example, and rather risk sending a task force on a somewhat hairy mission? Even taking in mind that this was a defensive war for the UK.
