[Gedrin]

I'd suspect a civil war or other significant social disruption as Germany collapses, at least economically. My guess is that with Germany being a power vacuum, it gives space to Soviet expansion. There's a East/West war, probably pretty close to on schedule. Poland, being the Euro/Russo invasion superhighway, get's flattened. Germany forms the front lines in another war.

We still get Churchill and Chamberlain, but Churchill will be older, and at an age where it might be significant (though it's possible the war would just invigorate the guy). However, depending on the timing, and the relative confidence of knowing that they'd smote Germany, Chamberlain might not hold on to office as long. I think the Russo/Euro war would break out before Churchill would be out of the picture. I'd say it's a toss up as to if the British Empire is in a better or worse position, relative to the Soviets.

FDR might not be alive when WWII starts, but I'd guess yes. Depending on timing, he might not be in office, perhaps even no third term. I've not studied the political alternatives in this time frame. Intervention in the new WWII would follow the same pattern; fund allies, gear up, come in when most advantageous or when needed.

The biggest difference will be the war itself. A Soviet expansion across the northern European plain, pre-blitzkrieg and with a lower industrial capacity, would be slower. Early Soviet expansions would be aimed at gaining strategic depth and industrial capacity (since that's what happens when Russia expands). War could be prevented by bolstering Germany as a bulwark against Soviet expansion, evolving into a familar East/West Cold War (but probably with British Empire holdings remaining intact and evolving toward quasi-independence). Of course, everyone might just say "screw the krauts" and then we're back in France.