It's a little far fetched. Why wouldn't Herman Goring be on that Sub? Hitler didn't want to kill Goring for treason more than a week before he supposedly committed suicide and by then, the fate of the war in Europe was sealed. Was Martin Bormann on that sub as well? Goebbels was the most loyal to Hitler. If the plan was to flee, he wouldn't have went the cyanide route.
I have a hard time believing a guy like Hitler or any of those other Nazis generals could just suddenly go live in peace. Even if they knew they lost the war, it does not seem likely they would go live in peace after a defeat.
The 3rd Reich would have needed to construct and operate a massive navy and even in the scenario of "Hitler does not invade Russia", by 1944 their resources were already stretched to the breaking point.
The manpower and other massive resources to keep multiple foreign countries enslaved would serve to absolutely prohibit significant further expansion
Build a massive navy without it being immediately attacked with full Allied support....no way