The tricky part seems to be twofold. First you need to avoid other powers that are friendly to the rich you have removed that will try do destroy you. This has also happened in failed revolutions like in Germany, Spain or the rest of the springtime of peoples. We could even consider the Napoleonic wars against the French revolution an instance of this. The only solution I see to this is again having the support of the military.
@MxVerda @sjuvonen @tinker
Finally, if you have not been destroyed by your capitalist enemies, the only problem is how to avoid becoming a capitalist yourself after you gain power. This is what in my understanding led to the USSR demise with the apparition of the Nomenklatura or the capitalist "communism" from China. Still, it can be argued that at least those systems ended being softer versions of capitalism that the ones that replaced, so it was not all in vain, but still.