Cs, despite the work of Lubavitch in Russia, yiddishkeit was not “kept alive.” If you don’t believe that, check out Brighton beach and see how many frum people there are. Not a lot. 99% of Russian jewry totally were and are secular.
And others worked on their behalf too, including rav Yitzchok zilber, as mentioned earlier in this thread. He taught Torah in secret, and anyone who is frum either had him to thank or chabad, or both. Usually the latter.
And it’s unfalsifiable that the Lubavitcher rebbe killed him. He could say he was doing something in shomayim; I’m sure he did what he thought was some sort of kabbalistic act. But do you think other tzadikim weren’t davening for him and Russia to fall? How do we know any more than, say, if a televangelist had made similar claims?
I looked up the doctors plot. Historians are not clear on the details, and there’s no direct evidence that stalin was planning genocide against Jews. On the surface, it is agreed upon that it was a plan to purge the communist party of people stalin didn’t like, and 6 out of 9 of the doctors accused were Jewish. I don’t know if that’s sufficient, because many doctors are jews. There are only second hand accounts of stalin planning to deport jews or worse. And one report says that he wanted to deport them all to the Jewish Autonomous Zone, which actually would have been a net gain, because they probably would have not intermarried and would have been able to stay frum, to an extent.