Unless Barbarossa is launched earlier, the Nazis defeating the Soviets is next to impossible.
However, if Hitler was able to win in Stalingrad, take Moscow, and push the Soviets behind the Ural Mountains (by some miracle), then there is almost no point for D-Day. The UK and US will see that the Nazis have taken over an entire continent (sans Iberia and Italy w/ client states) and prepare to fight a solely defensive war if the Nazis decide to go on the offensive against the Western Allies.
Without a western front, the US and UK more than likely focus on Japan assuming nothing changed as a result of the Nazis "defeating" the Soviet Union. The Japanese will launch attacks into Siberia, however its success is undetermined. Either way, the Japanese will be forced to deal with more Brits and Americans in the Pacific.
After the Japanese are presumably defeated, the US and UK are forced into a Cold War against the continental Third Reich. I'm not sure if they would go to war at a later date (if Hitler lives much longer than OTL its very possible), but if there isn't, then the Nazis will probably collapse similarly to the Soviet Union iOTL.
That's just my (rushed) two cents.