If D-Day, failed, Russia wouldn't miraculously gain all the same territory they did in OTL, then more. The whole point of opening a second front was to force Germany to spread its resources thinner. Sure, Russia was already winning in the East, but it's not like they were strolling through the German lines like Darth Vader through sand People. There was strong resistance.
After the D-Day landing, Hitler sent a large force West to fight the Allies, resulting in weakening Germany's Eastern Front - stupidly, I might add. During Operation: Market Garden, Hitler actually ordered such a large counterattack on Allied forces in Holland that he put Germany's own security at immediate risk. An Allied attack on Germany itself, ignoring their own bogged down troops in the Netherlands and Belgium, would have taken large swathes of Germany. It was successful, but stupid, action by Hitler. And it took even more troops from the Eastern Front, as did the Battle of the Bulge.
If the Normandy Invasion failed, Roosevelt would likely remove his head from his buttocks and follow Churchill's plan to attack via the Balkans. However, this would take a lot of time, and many new troops to be shipped from the US. In short, it would be a logistical nightmare, never mind the morale boost to the Germans, and simultaneous slump among the Allies. You could also expect British-American violence to increase amogn the rank and file, with both sides blaming the other for the loss, compounding the difficulties. Then there's De Gaulle's Free French, who would be, shall we say, less than impressed with America and Britain, as if Charles needed more reasons to dislike them.
Meanwhile, in France, the many resistance fighters who rose up and began sabotage operations and open revolt against the Germans would quite quickly end up dead. Also likely would be a massive crackdown by the occupying army, leading to even more deaths among the civilian population.
In the East, Russia's progress would go more slowly. Also, since a new landing in Normandy would be completely ruled out - no-one attacks a seemingly impregnable position twice, especially when there's an easier option available - they'd probably concentrate more in the North than the Balkans themselves. After all, Stalin was no idiot, and he already had an agreement with Britain to split Eastern Europe. Why fight for the Balkans, if the Western Allies are going to take them for you?
The question is essentially how long it would take the US and Britain to mount another invasion, this time of the Balkans. They'd likely take more of Italy by the end of the war than they actually had, and the war would take longer, regadless of how long the new operation took to mount. But the extra time would also allow the Germans to create more of their new technologically superior weapons, such as new jet fighters/bombers and long-range rocket systems. it would also bring the US closer to completing the A-bomb.
I don't see the US dropping said A-bomb on Germany without sufficient reason. After all, let's not forget there's a huge difference between Germans and Japanese: They're not Asian. German-Americans weren't put in internment camps for the duration of the war. There were considerably less German women raped by Americans than Japanese (particularly Okinawan) women during and after the war. Unless the Germans were putting up an ungodly fight, or the Russians were gaining a significant enough advantage to warrant a 'demonstration' in Europe, I don't see America usuing nukes on German civilians. Purley military or scientific targets... Now that's a possibility.
All-in-all, I don't see the Russians gaining too much of an extra advantage. Let's remember, Russia never once overstepped the bounds of their previous agreements as regards to territory. While they were happy to steal German territory both for themselves and Poland, all of that territory was inside the sphere of influence which Stalin and Churchill had already agreed upon.
If anything, a prolonged war would have resulted in a weaker Russia, although the US and Britain would also be weaker than OTL, and France would be devastated. On the plus side, the slaughter of resistance groups in France might keep Socialists from coming to power in that country, and De Gaulle would almost certainly do a better job of rebuilding than they did. That's a pretty piss-weak positive though. Honestly, I don't see much difference, except in the casualty numbers.