"FDR was assassinated…?"
Tell me that was a typo, please!
Zangara did kill Chicago reform Mayor Anton Cermak, but didn't hit Franklin at all, though not missing him by much.
And, regarding Adolf, of course the bastard had it coming, and the war ending in the Summer of 1944 would have saved literally millions of lives, but Europe would still have been split up pretty much as it was, the Cold War would still have followed, Berlin divided, etc, so the future would probably not have been significantly different--except for one thing.
If Uncle Adi had been assassinated in the July Plot, almost immediately the speculation--in Germany, where it would count--would begin that his death prevented him from turning the war around at the last minute. With V-Weapons in hand, and more coming, it would be said that his "genius" could still have saved Nazi Germany at the last minute--and where would be the PROOF that such beliefs would be wrong?
Arguments against such an outcome would be many and powerful, of course, but not to those who would cling to the idea of Germany--once again!--being "Stabbed in the back," and forced to yet another humiliating peace with millions of their soldiers still in the field.
In short, a sudden end to the war would create the very atmosphere that 20 years later might well have given the neo-Nazi's of the 1960's the impetus actually to re-achieve power.
Those of us old enough still remember the magazine and newspaper articles in the early to mid-60's "predicting" Germany would go back to a far Right government bent on revenge, and that was when, in retrospect, there was actually very little chance of that happening.
I still shock myself when I say it, but in the end, I have come to think it's best the Pig From Braunau survived the bomb plot(s) and took down Germany--and Nazism--with him a sea of blood and fire. No myths of the Wehrmacht or Hitler turning the war around, no question but that Germany was utterly defeated and made to face its guilt and suffer the consequences. That was the only way to end not only the war, but it's most immediate cause. Dying early would have been Der Fuehrer's dream if it meant his ascension to the pantheon of German Gods--one of whom could yet return to birth the "Fourth Reich".
Cold comfort, I well understand, to the millions still to die in the camps, fire bombings, and combat to come in those last 10 months of the war in Europe, but their graves have been the foundation of 70 years of general peace since, despite the repeated best efforts of one half of the Victors to experience it all again--and still do today.
TVAG