If the Hitler had possessed enough wisdom/restraint to postpone or cancel Barbarossa despite his ideological hatred of the Soviets then the odds of a D-Day type landing being possible would have been way, way smaller and short of a nuclear bombardment of Europe the Nazis may never have been defeated. Even if they had been, they might have been able to negotiate a conditional surrender. It's one of the weirdest, darkest historical hypotheticals and it was avoided only because Hitler wasn't just a little wiser.