To that point, the war was already over when Allied forces landed in France and forced Germany into a two front war. I suspect that if it wasn’t for D-Day including Omaha landings going well, Germany would of simply pounded the Russians until they had nothing left but rocks to throw at the Germans.
The "two front war" Began with the war in North Africa, Sicily and t hen Italy.
D-Day only was the beginning of a second front in Northern Europe. but by then the Germans were already fighting the allies on two fronts. In north Africa alone the Germans lost almost a million troops killed and captured (about 620K killed and wounded and over 250K captured) In Sicily the Germans suffered about 30K killed or wounded and another 100K captured, German suffered over 300K more casualties in Italy not including those captured.
All those took away much needed forces that could have been used against the Russian forces. Not to mention hundreds of tonnes of fuel, food,medical supplies, aircraft,tanks,aircraft, and untold amounts of other war material that was not able to be used against the Russians