My honest opinion after reading the newspapers of the era. The WAllies would have accepted under the table conditions for occupying Europe as part of a battlefield armistice of German forces in the West. They would officially keep their position that they will accept nothing less then unconditional surrender while they quickly occupy Germany and large areas of Poland and then the official unconditional surrender would be announced. Stalin would be pissed off, but there would be nothing he could do about it short of WW3 which he wasn't ready for.
FDR knew a failed D-Day would potentially kill his re-election bid and that Rommel was willing to give him an out if he agreed to a battlefield surrender where the British and Americans occupy Germany and avoid some of the more extreme plans being discussed at the time like Germany being reduced to substance farming.
The papers in England and the U.S. at the time even talk about hammering out the armistice terms as well as debates over how flexible they should be about the terms if things don't turn out well with the invasion.
Rommel wasn't stupid he knew Germany was screwed win or lose at Normandy, but success would win him the support of the armies in the West so that he hoped he could sit down with Monty and Ike and hammer out the terms sort of like Lee at Appomattox only secretly under the table.
His failure in the West meant he didn't win over the support of the army to take executive action on his own at least while Hitler was alive and that was key at least according to what British intelligence found out in late 1944 and early 1945 in wiretapping German generals was why Rommel changed his position late in the day from wanting Hitler put on trial to wanting him killed as Hitler living and being able to countermand his orders was standing in the way of Rommel ordering an armistice in the West and ending the war in the summer of 1944.
I think in talks about Normandy people often forget that the commander of German forces in France.
A. Knew the war was lost before the battle.
B. Was willing to take executive action to see Germany occupied earlier and the war end earlier.
C. Had a string of very bad luck that kept him from being able to effectively take command of all the forces in the West and be able to end the war about a year early under better conditions for the German population.
D. With a few changes to the timeline he could have gotten the kind of support he needed to order an armistice in the West.
This would be a timeline where he would have the kind of support with the officers that would be needed to take executive action in the West to sit down with Monty and Ike and if FDR and Churchill agree it would effectively end the war in 1944 millions of lives are saved, Germany still gets occupied, the Nazi leadership still kills themselves or gets hung, but things would be quite different and the Western Allies in a much stronger position visa via the Soviets in central Europe during the Cold War. It would also end the Final Solution before the worst months of it occurred when the SS went all out trying to finish what they started.
