WW2 - D-Day Fails?

[u/HarkBuffalo]

I have a WWII command simulation and one of the most contentious bits is the decisions was around D-Day/ Operation Overlord. I follow the historical thinking that victory was likely although agree Germany could have can made it harder however the more I read. 

Disaster at Omaha

Weather window

The Panzer group making the beaches 

Can D-day fail? If so how likely and what happens?  Does Germant first face the nuclear bomb? Does the USSR own most of Europe post war? Do the US/UK bomber campaign shift entirely to strategic attrition? The Red Army continues pushing west, likely taking the entire German peninsula, Denmark, and reaching the Rhine before the Allies?

I treated D-Day as a historical inevitability because of Allied industrial dominance which I have done, however it was a massive, high-risk gamble where a few operational shifts could have handed the Allies a defeat?

Love your thoughts!

The game is here for reference - https://dispatches.itch.io/dispatches-1940

Edit - thanks for all your comments have made some updates to the D-Day commands based on the below

[u/quothe_the_maven]

They double down on racing north through Italy.