If we run with my PoDs... the Soviets could avoid the crippling damage to their breadbasket and would have the agricultural resources to supplement local production enough to feed continental Europe. They had kinda already done once it before. German occupied Europe would have been crippled by famine in the winter of '41/'42 had Stalin not opened Soviet granaries to the Germans and supplied their tractors with so much oil... not because he was a nice guy (even typing out that fragment made me laughs) but because he was trying to buy off Hitler from invading him. Obviously didn't take. But it does show that a Soviet dominated Europe would have the resources to feed itself... at least for the short-medium term.
A 1942 or later PoD, on the other hand, tosses that out the window. The Soviets would be hard pressed to feed all of Europe after the devastation of the OTL Barbarossa. Even as it was, their efforts to feed Eastern Europe in the winter of '45/'46 contributed to a major famine in Soviet Central Asia.
How about this:
- FDR dies prior to 1940, the New Deal coalition fractures (ala '48) and an isolationist Republican (Wilkie?) becomes president. He never decides to fund any fancy Manhattan project.
- Japan and China are not at war, meaning no need for Japan to go ful Pearl Harbor. Either because something happened in '36 that kept the militarists in check, or because Tokyo's efforts for peace in '38 won out over the militarists, or because the Soviet Union attack Japan in that time span, forcing it to the negotiating table, or something. Whatever it is, the Japanese are left in no position to awaken the sleeping giant.
- Soviets prepare for an attack on Germany and actually do so after Dunkirk. French fight on, causing more losses from attrition to the Panzers, before finally being driven out.
- lack of trade with the Soviets crashes the Nazi economy and war effort
- Germans counterattack, but the Red Army handles the situation comparatively better (maybe that short war with Japan led to them fixing some of their flaws), "only" losing ~1 million men to encirclement, and are in Berlin by early-mid '43
- British and French return to the continent, but Stalin will have none of it, and advances all the way to Gibraltar
They can't take out Britain, but Britain can't take them out either.