If it had 'only' lasted to the 60's/70's, it would have killed far more people, and without the sharp, comprehensive ideological defeat of fascism, and decades of children being indoctrinated into it, even if it failed, you'd still have hundreds of thousands to millions of hardline adherents.
And this is presuming they did not develop nuclear weapons, which they were painfully close to throughout the later years of WWII, and allied intelligence was desperately trying to prevent. If there had been hot war on and the Nazis got their hands on nukes, the amount of destruction would have been mind-boggling, and almost certainly ended with American nuclear weapons being the tool that ended the war in Europe.
If the nazis had been willing to nuke the allies, but the allies weren't willing to nuke the nazis, then horrific amounts of Europe might have ended up under mushroom clouds.