Even had Germany somehow kept the knowledge, it had, at best, a very brief period of time between the beginning of the war and the period when its industrial capacity was being seriously strained, if not bombed almost continuously, to work on the weapon. The Nazi nuclear bomb project was also underfunded for political reasons, not to mention the fact it would have been very difficult to justify working on a blue-sky wonder-weapon instead of building more tanks and planes and rifles for the three-front war practically at their doorstep.

You can try to posit a Nazi regime without such constraints, but a Nazi regime which isn't lead by Hitler is fundamentally different from the regime we're talking about. A well-run Nazi Germany, one which didn't pick unwinnable fights, is a Nazi Germany contrary to Hitler's vision.