Very interesting. I would only quibble about your second point: "Zelensky will not stay in power."

This statement is true of all leaders. But I disagree with the first phrase of your second sentence. Once it is clear that militarily Ukraine cannot win (your first point with multiple scenarios how it becomes clear), it will be in Russia's interest that Zelensky is in power to surrender, and in the West's and Ukraine's interest that Zelensky dies suspiciously. His death will be called a muder by Russia, so that when Zelensky's replacement surrenders the replacment can be branded a "Russian puppet" and probably also killed (and also blamed on Russia).

This "egregious act of assassination" would be used by the west to pressure NATO members to ignore membership requirements and let the remaining part of Ukraine into NATO, even though I expect that the documents signed by Ukraine when it surrenders will explicitly say Ukraine will not join NATO.

My very cynical two cents.