I agree the Western Front was needed for this, as well as influence in Germany. I think Germany could have made a much stronger attempt at defense of the homeland if they didn't have so many forces tied up in the West once the front constricted in length when Warsaw was taken. Instead of making their last push against us at the Bulge they could have tried it on the Eastern Front.
Hitler really blew it by pursuing a two front war, to state the obvious.
At most, the failure of D-Day would have slightly delayed the inevitable Soviet Victory. After the Soviet Victories at Stalingrad and Kursk in 1943, Germany had lost too much war material that it couldn’t replace anywhere near as quickly as the Soviets could and with the loss of the Romanian oilfields a couple of months after D-Day, the Germans lost their only major source of oil, which catastrophically limited their ability to move and provide air-cover....