in the run up to the 1944 election the party leaders in the democratic party did not want Henry Wallace to be FDR's running mate as they thought he was too liberal. Roosevelt eventually agreed to replace him, and Harry Truman was selected. However he didn't want the VP slot, he had to be convinced, IIRC the party leadership allowed him to "overhear" a phone conversation where FDR accused the Missouri Senator of dividing the Democratic party by not accepting the veep nod. This led to Truman finally accepting the nomination, but what if it is not enough, or he sniffs out the BS? Either way, Harry Truman does not accept the veep nod and someone else has to be put in as FDR's vice presidential candidate, and eventual replacement
Who would have gotten picked next? Assuming that FDR dies at the same time as OTL, does this vice president also elect to drop the bombs on hiroshima and nagasaki? How do they face off against the Soviets in post war Europe? Does the Korean war still happen? Does Vietnam? What else happens?