As always, I must start by saying I have no expertise and there is no reason anyone should be particularly interested in my thoughts.
The question is how will the war in Ukraine end. I guess I have a guess, but it implies it will last a long time.
I can think of 3 possibilities, Russian victory, Ukrainian victory or a negotiated peace.
First, I think it won’t end with Russian victory. Given recent Ukrainian battlefield victories, this sounds obvious. I think also that even if the Russian army were to defeat the Ukrainian army (as I and many others expected at the time of the invasion) the war would not end, but rather shift to a guerrilla war of resistance. It is clear that even a battlefield victory would require Russian mobilization including sending draftees. That seems unlikely.
I think a Ukrainian victory is possible. By this I mean a withdrawal of Russian forces to the internationally recognized borders. Some Ukrainians have discussed reparations and prosecution of war criminals. They are not being reasonable. Ukraine certainly won’t cross the border into Russia to obtain either.
I do not think that Vladimir Putin will ever accept a complete Ukrainian victory. I see no reason to hope he would. I think this outcome depends on removal of Putin through a palace coup, assassination, or death by natural causes. At that point the new Russian leader (or junta) might withdraw. Importantly, I think a hawk who advocated invading Urkaine would do that (and lie about the earlier advocacy).
I don’t see much chance of any sort of negotiated compromise unless there is a major battlefield reversal. FIrst it would amount to a defeat of Putin, and he won’t accept it (see above). Second, the vast majority of Urkainians wouldn’t accept it. I can see only one possible compromise — a Crimean referendum conducted by the UN. I am not Urkainian, but I see no problem with this. I also think it possible that Crimeans would vote to join Russia (here one problem is that the electorate has to be people who lived there when Russia forcibly annexed Crimea with no vote for people who moved from Russia to Crimea after the annexation). This seems unlikely. I don’t think Ukrainians would accept this. I am sure Putin wouldn’t. I don’t see why any Russian replacement regime would. In particular, I see no chance of a return to the status quo ante when Crimea was part of Ukraine but the Sebastopol naval base was controlled by Russia. That didn’t work, and I don’t think Urkaine would accept it.
In any case, this compromise would only be possible if Putin were removed (or killed). I don’t see how that could happen any time soon, and I expect the war to continue for a long time.