I was reading about Nazis fleeing the country (many to South America), obviously plans were in place long before Hitler's final days in his bunker in Berlin. When did most high ranking Nazis realize they had better have a Plan B because the war would be lost? Obviously many couldn't voice this opinion but with the benefit of documents, letters, hindsight, etc...when did they begin post war plans because they knew there would be no Third Reich in the future?
I would suggest the book Five Years, Four Fronts by Georg Grossjohan. While I do not remember if he has a specific "aha!" moment about the state of the Reich, and what his plans are for the post war. Towards the end of the war he does begin making contingency plans, but not until the very end. Grossjohan does explain the gradual realization that the war is lost or being lost and what comes next. While he is only one man, it does offer an interesting look into what the Junior officers were thinking about for the end of the war.
While not in the question above, Grossjohan also does a pretty good job of explaining the mindset of junior officers throughout the war, and how blatantly they could see what was coming.