It doesn't matter how many people they would have had, the communist system would have collapsed regardless. You only need to look at China with it's more than a billion people and it is not more powerful than the US to know that population, while important, is not the determining factor.
Communism is a failed ideology. But Russia would have flourished even under a communist regime, as it had a strong base (literate people, productive population, vast amounts of natural resources.etc).
Those two don't work together.
