Yeah, if the Allies had invaded Italy in 1943 instead of Greece the Italians would have surrendered pretty quickly. The Italians would surely give up once Southern Italy was invaded even if they hadn't had Soviet forces closing in on them from Austria, and the Allies from Southern France.
If the Soviets had focussed more on reaching Berlin rather then secure the Balkans during Winter 1944-1945 and declare war on Japan in April, a nuke over a German city could be prevented as the Soviets entering Berlin would end it before the American have their nuke ready, i'd say mid-May. Japan, not being occupied by the Soviets from the North will get the bomb instead and surrender last.
At least, thats how i see it happening.