Hmm, I honestly doubt that the Wehrmacht, in 1944, had any chance of throwing off D-day. Sure, Omaha was bloody, and the forces there were stalled for more than 24 hours, but the defending German troops took serious losses during that time as well, and retreated to avoid complete destruction, allowing a quicker advance there then at all the other invasion beachheads afterwards. And while the invasion was contained in the Normandy for almost 2 months, once the Allies broke through, there was nothing left to stop them from liberating all of France.
The Wehrmacht, the Kriegsmarine, and the Luftwaffe simply lacked the resources to fight the Allies effectively for a longer time. To defeat an invasion, the Wehrmacht would have had to have the capability to smash all the beachheads, while the Luftwaffe and Kriegsmarine would have had to be able to drive the Allied invasion fleet off, or at least make their staying at the French Coast too costly. As the Luftwaffe and Kriegsmarine definitely lacked that ability, the Allies could resupply at will, while their Air Forces could prevent the Wehrmacht from shifting their meager reserves to meet the threat. So a defensive victory at D-day whould have required something close to a miracle or two.
In the east, an armistice might have been possible up to early '43, though I lack the knowledge whether the Soviet advances contained suggestions about future borders, or whether an armistice would mean returning to pre-Barbarossa borders.
But ever since Stalingrad, and especially since Kursk, Soviet superiority was rather clearly established, especially as they had less problems resupplying their front with material and men. So I'd say they had nothing to gain from an armistice that would leave Eastern Europe under German control, and to get countries like Poland, Romania or Hungary to recognize the USSR as their master, the Red Army had to liberate them. So why should the Soviets have agreed to an armistice that would deny them a chance at empire-building? Loss of life surely didn't figure into Stalin's considerations.