Unfortunately, AskHistorians only deals with what did happen, not what might have happened and I've therefore had to remove your post. However, your question would be perfect for /r/HistoricalWhatIf, should you wish to cross-post.

Not sure if this is the best place to ask, since it's more of a common alternate history question. As to an answer, the best explanation I've heard so far comes from former Pentagon planner Stuart Slade. He postulated in his novel The Big One that the best scenario for Germany was the success of the Halifax-Butler coup causing the capitulation of Britain, denying the US any airbases closer than Iceland or Russia. Hitler's megalomania would almost assuredly result in his demise from a coup, but there were enough hardliners that the war could continue even without him. Complete conquest of Russia would be nearly impossible due to overextended supply lines, but the situation for the Russians would still be nothing short of a meat grinder.

Regardless of Germany's success in Europe, their lack of development on the A-bomb would be their undoing. The Convair B-36 "Peacemaker" was started as the ultimate bomber project of WWII, with the ability to reach Germany from Continental US airfields and almost complete invulnerability to the air defenses of the era. It never saw use in WWII, but if Germany stuck through until 1947 it could have seen use in one of the most horrifying contingency plans ever dreamed up by the Pentagon - The Big One.

According to Slade, there were two options for deploying the A-bomb against Germany, which fortunately surrendered before they were seriously considered in real life. The first called for deploying devices as they came off the Manhattan Project on B-29 bombers. This would have placed the first deployments on a similar timeframe as the bombings of Hiroshima and Nagasaki. It would have also allowed the Germans, once the shock had passed, to furiously work toward countermeasures to the B-29. It was called The Little One.

For those reasons, the Pentagon planners instead favored the alternate scenario of a massive, overwhelming strike called The Big One. This plan called for the stockpiling of nuclear devices until a suitable transcontinental delivery system (the B-36) was ready in sufficient numbers. At US buildup levels, that would have worked out to mid-1947. The bombers would then, in a single, massive airstrike, systematically destroy every major industrial and population center in Germany.

The results of so many nuclear airbursts would probably not have been completely cataclysmic, but it would have made the Chernobyl fallout look like a firecracker. Most of Germany would remain uninhabitable to this day, with hot spots scattered all over the countryside. There would have been several years of near-famine worldwide due to global cooling and irradiated crops. Nevermind the near-total eradication of an entire nation.

Again, most of this is conjecture and extrapolation based on Slade's interpretation of Pentagon plans. I don't know if more plausible scenarios exist.