FDR could easily lose in 1940 and it would not impact WW2 as we know it up to that point. Wilkie is the usual suspect due to OTL but not impossible that Taft or other isolationist could win. That is certainly plausible and not some pod that makes ww2 as we know it implausible .
UK would be worse off initially but not certain that the Japanese still don’t attack US, so that could still bring them into war. Even if Wilkie were to win, he wanted to avoid war but still supported idea of lend lease. So I guess i am not understanding this statement you made?
Willkie was at LEAST as interventionalist as FDR, possibly more so.
Just saying "Willkie wins" doesn't get you what you want. In fact, a Willkie win won't.
Turning to the scenario, as ever, its the usual two sentences and no background and OP has run off.
How and when is the Soviet Union defeated? 1941? 1942?
What is the state of the surviving Soviet government east of the Urals? Cohesive, still engaged in skirmishs along the Eastern front, along with massive partisans in the occupied Soviet territory? Or a complete collapse and little partisan activity at all?
What is the state of the United States?
Who is the President?
Is Lend-Lease in effect?
Is the United States at war with Japan?
Is the United Kingdom also at war with Japan?
If so, is the United States supplying vast war material to the UK on the pretext of 'helping them fight the Japanese' whilst all of it is instead being used to fight Germany and the US doesn't really give a hoot that that is the case?
What is the status of France, Vichy and/or Free as the case may be?
If the Soviet Union is behind the Urals, but still engaged in heavy skirmish activity and trying to build up, along with significant partisan activity in the occupied Soviet Union; along with a UK-US alliance against Japan, then no, I don't think the UK will give up and indeed, in the long run the US will end up in this war and Germany will get buckets of instant sunshine come late 1945.
If the SU is virtually gone, the US run by Robert Taft and Charles Lindberg and the UK-US don't have any alliance against Japan, then yes, I can see the UK being forced to the table.
But the first scenario is vastly more likely than the second, and I wouldn't even know how you'd realistically get to the second.