A lot was cased by Hitler's paranoia. Once he's gone I see a more sane distrobution of control.
not really, since the various power blocs will all be scraping whatever power they can get in a post hitler germany.
Hitler can, if he's able, decide his successor. In OTL that was generally Goering. By 1950, Goering's Luftwaffe has failed to defeat Great Britain and has a mixed record. In comparison, the Army has been merged into the Waffen SS, which means that the SS is now both the men who won the war and the men who won the "peace" as it were.
So, the leader to replace Hitler is probably Himmler; Heydrich may very well get Himmler's former office as head of a bloated SS. Born in 1900, Himmler would be a decade younger than Hitler. The man who launched the Holocaust, the efforts to Germanize Poland and the former Soviet Union, etc, isn't going to stop just because he's in charge.
There will be major resistance to Himmler/Heydrich winding up in power. But with the Army and the SS in their corner and the radical ideologues on their page, I think they win. Goering gets a ceremonial Presidency. Military leaders, like Model, can perhaps aspire for some sort of defense secretary post. Moderates and those not buying into Nazist behavior, like Rommel, probably retire and possibly emigrate.
I could see Siegfried Rommel choosing the USA over Nazi Germany.
There's perhaps no long term way to ensure the high life for the Germany people, but in the medium term, squeezing the Vassals, further small conquests (Sweden, Switzerland, possibly Turkey) will continue the empire, and the prospect of free labor until the slavs run out might do so longer.
We won't be so lucky as to have a Wehrmacht/SS Civil war, or a very moderate figure replace Hitler. The man who does is very likely to have earned his stripes doing and running many of the things that make the Nazis evil. They will not turn away.
Does it end in the 1970s? The 1990s? the alterative future? I think they can last a good long time with all the people they have to exploit and resources at their disposal.