lol, the Soviets is a land made up of many different nationalities, it's a country closed off to outside influences, it's a country that pretty much just took the eastern half of Europe in WW2, and it's poor as well as not improving economically. by the time it collapsed it's so poor it can't even finish it's military projects.
China has the largest foreign reserves, it's economy is fast expanding (regardless of what you think China hasn't fallen, don't predict it, or it'll make you look as stupid as Gordon Chang, his every 6 month China collapse theory has been going on for a while now), China has 91+ percent of just Han Chinese, break up? Into what? We are one and no one wants to be individual countries, what would we even call it? There's never been separate countries before.
Whether Tibet and Xinjiang is ours or not is not relevant, they want to be with us despite what some separatists and Lama wants you to believe. How do I know this? Simple, have you seen what Islamic separatism actually looks like when there is popular support? This is like calling a spilled drink a flood. Besides even the Lama don't want to separate anymore, why? He sees the opportunity they have with China rather than become like one of those break away Soviet states, can you even name one?
Soviets met the fate because of too many different nationalities, not a problem in China, just one. Failed economic polices, you want to see what it actually looks like? Look no further than all of the developing world other than China, a communist country, ironic isn't it. There's also political instability which contrary to what you think doesn't exist, I would again point to Chinese civil war, and Arab springs to what real instability looks like.
Oh and US did work on a plan to separate China, it failed multiple times. Just like Napoleon, US cannot imagine Chinese love their country as much as Americans love theirs. Much like the Afgan conflict. Except you know worse.
Lastly, everyone in China supports Chinese claiming of the seas. Support for China's rise is at a all time high in China.