Hmm. But:

If the allies had been pushed off the beaches in June 1944, the Germans would have known there could be no invasion in the west for at least another year. (Due to a combination of a need for good weather and the sheer lead time required for planning)

They could therefore safely have stripped NW Europe pretty bare of troops until, say, May 1945. Also, presumably, most of the Norway divisions could also have been redeployed, since it would have been clear there could be no landing in Norway either.

IIRC the Soviets were actually closer to the limits of their available resources and manpower than is generally realised by the end. With the extra divisions available possibly the Germans could actually have held them off. Presumably also the Italian front could have been held static.

I can't see the allies nuking Germany in this case, since that would hand the continent to Stalin.

The big unknown are the politcial ramifications. Churchill was seriously worried about the effect the V2's had on civilian morale in London and if the D day failure was sufficiently bloody, would there have been any appetite for another go in 1945? if the Russians were fought to a standstill in Poland in 1944, with no second front and no promise of one in 1945, would Stalin have offered/accepted a separate peace? Who can say? But some sort of armistice leaving Nazi germany intact and in control of NW Europe must have been a possible outcome. And once the Soviets had made peace the western allies really would have had little prospect of taking western Europe.