Three months after the surrender of Germany, the USA dropped nuclear bombs on Hiroshima and Nagasaki. If Germany had not already been defeated the USA would done the same to Germany.
If you look at the condition of Russia prior to World War II, you would realize why Hilter thought he could defeat Russia. He expected it to fall apart, it almost did in World War II The Soviets executed 158,000 soldiers for desertion. A good friend of mine surrendered to the Germans and then fled to america after the war because he would have been killed if he went back to the USSR, He was from Tibelisa, the soviets had confiscated his familys property and kill a number of his relatives.
Take into account:
Joseph Stalin - Wikipedia, the free encyclopedia
What defeated Hitler was a two front war, but even with out Russia, Hilter defeat was inevitable , the same as Japan.