In a word, they'd have gotten smoked. For many of the reasons you stated, yes. And that would have happened quickly. Also by November 45 the US had sufficient atomic bombs to start using against USSR.
The Soviet Union got most of what it wanted by occupying Eastern Europe and then politically...at first. The Comintern had infiltrated much of the Western European resistance movements as well as the trade unions. The Marshal Plan was as much to forestall the latter effects more than a desire to restore Europe.
It'd be bloody but in the long run the Soviet Union probably wouldn't exist west of the Urals, North Korea never would have come to exist, and Curtis Lemay would have been unleashed on the USSR.
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