Just read an article in a mil hist mag on this ABWEHR attempt to assassinate all 3 Allied leaders during the 1943 Tehran Conference- WI they'd been successful ?
The replacements are interesting - Wallace, Attlee (perhaps temporarily) and Molotov (again, perhaps temporarily
"President Wallace" should sound pretty terrifying to anyone who's read the TL, "For All Time", even if said TL was written entirely with dystopia in mind.
As for the "temporarily" do you mean to suggest there would be some kind of internal Soviet power struggle for succession?