Japan is broken, a failed D-day will not help it one bit and continued pressure and defeats on all sides shall continue.
Germany? It rather depends on how D-day is crushed. If the initial landing forces fail to capture the beaches and a driven into the sea, its a tragic but hardly catastrophic loss. The continued threat of other operations (weather permitting) would keep the substantial german forces in place, implying that the Red Army would accomplish much the same as it did in OTL. Another assault across the channel shall likely liberate France before the red army can cover the distance.
Anyone playing the odds would have to bet on the allies. On the other hand however nothing is out and out predictable in war.
If however D-day is a reasonable success for the first couple of weeks, ensuring substantial allied forces are in france when a German counter attack appears. If such an attack was a crushing success which drove to the coast, somehow bringing about the loss of every man, gun or other peice of equipment for the Allies then things are suddenly quite different.
Well.. not that different really, but it gives Germany probably one last major attack to use on the Russians. This might ensure that Bagration isn't such a crushing success but in reality it is unlikely to allow Germany to take the iniative. All of Germany eventually falls to the USSR, however France is liberated by a fresh assault across the channel later that year.
While dreams of a red Europe are amusing to contemplate, they are quite unlikely. In the time taken for the Red army to travel across Germany the western allies should atleast be able to liberate France, Belgium and you would have thought the Netherlands from whatever rag-tag german resistance remains. (Unless you reason a failed D-day causes a significantly faster Russian advance.. there shouldn't be any reason why there wouldn't be another attempt across the channel the next year)