Ahh, the old realpolitik argument. Better to have a stable brutal dictatorship, like, say Stalin, than a risky, unstable, unpredictable Democracy. After all, brutal dictatorships are so reliable in their actions that it gives comfort to the State Dept.
The devotés of realpolitik prefer the "stability" of an Iraq under Saddam to the risk of a failed Weimar. In 1938, you probably would have been arguing that National Socialism was an expression of natural equilibrium for the entity composed of "Greater Germany".
The problem with your outcomes that you outline is the Fallacy of False Dilemma. You go from "two most likely" to "second possible", denying the third through "n"th possible outcomes. Indeed, with the historical examples of postwar Germany and Japan having democracy thrust upon them compared with postwar East Germany and China with the "stability" of dictatorship, your analysis ignores the most recent large scale examples of success.
The stable dictatorship model has been tried in the Middle East for a hundred years, and is an abject failure. Time to do something that actually works once in a while.
Your points are good but I like to point out, least Stalin wasn't killing Amaricans.
Democracy for everyone was NOT in the cards. The choice was to ally with Stalin to defeat Hitler or ally with Hitler to defeat Stalin or stay away from the conflict. The first choice brought/secured democracy in Western Europe, the second and third would kill chances for democracy in the WHOLE Old World, and possibly in USA as well.
Do you get it?