On the one hand, he was extremely dedicated to achieving unconditional surrender. On the other hand, he was more willing to work with Stalin (afaik) than Truman, and Byrnes would never have become Secretary of State. Would FDR living to the end of WW2 have changed the outcome of the war with Japan?
FDR would have been less likely because he wanted to be Teddy Roosevelt, who brokered the Soviet-Japanese peace a generation earlier and he would want to do that too! other than that, he was old money racist and wasn't as fervent about killing foreigners without a clear profit as many other US presidents. he's also one of the main ones to do anything good for the general public, so I give him some benefit of the doubt.