The communists' atheism was as doctrinal and thoughtless as most people's religious views.
It's not atheism. I don't think true atheism based on personnal views rather than massive doctrine would come back to religious beliefs as soon as communism fell.
Atheism is about adding average 1 and average 1 and saying that it equals to average 2, and that while it could be 0, it's so very unlikely that it's almost statistically irrelevant.
Atheism is really scientific agnosticism, but we can't call it that otherwise we'd be confused with all the mystics.
You don't give up that kind of logic in the lack of empirical evidence of the opposite unless you didn't understand it in the first place and simply believed it as one could believe in religious theses.