The PRC has now lasted longer than the USSR. How did that happen?
I think there are two reasons. First, the PRC leadership was far more willing to show flexibility on economic policy than their Soviet counterparts. Admittedly, if the USSR had adopted a state capitalist, export-driven approach to prosperity, it would not have been embraced by the capitalist world, but a significant reshaping of the economy might still have been possible without giving up political control; after all, even Lenin was willing to tolerate the NEP. Second, the USSR wasted a lot of resources and a lot of international credibility trying to impose its uninspiring political and economic model on the rest of the world. The Chinese believe too strongly in their own exceptionalism to try that.