If the Allies take a loss at Normandy, fortress Europe holds and we enter a stalemate. The 101st and 82nd Airborne would be stranded behind enemy lines with no hope of resupply. At the very least many more casualties in follow up landing attempts. Nazis don’t get pressured on multiple fronts. A lot of things have to go right to end up with the same outcome. Not a lot of things have to happen for Hitler and Nazi Germany to remain a military power.
The Soviets would have still ended up in Berlin even if Overlord failed. Probably not by April 1945 but it was still going to happen. Consider that 90% of all Whermacht casualties in the war were inflicted by the Soviets. The importance of Normandy was that it enabled us to keep much of Europe out of the Soviet sphere.
I don’t know. A massive defeat at Normandy might have totally stalled the Allies. Second guessing is a bitch. Just look at Africa and Italy.
Meanwhile, the Nazis would have been riding high, had more time and resources to devote to the East.
Let’s say the Soviets roll them anyways (most likely)...if we aren’t meeting them in Berlin, do they stop? I doubt it. Now we are maybe meeting them in Paris? Do we stalemate or do we fight them now that they’ve violated our alliance by invading France (under the pretense of wiping out remaining Nazi units/leaders)? Either way, seems much worse than the way it played out.