All of this is certainly possible, but I don't think how it will play out for a few reasons.
1. Putin can ill afford to lose Crimea, really under any circumstance. Losing Crimea = certain death for him. He won't give that back under any circumstance and will have his people fight to the death to keep it. I don't think there is any level of propaganda he could use to justify it's loss. If there is a hill to die on for him, it's Crimea.
2. In so far as the Donbas is concerned, he could easily make the propagandized claim that it has been de-nazied and leave. The general Russian population could be convinced of this and it could be sold as a security victory/mission accomplished bullshit. They'd buy it. That having been said, he's shown absolutely no interest in doing so thus far, and there is nothing that indicates he has any intention of changing his mind.
3. I do think Melitopol is Ukraine's next move, which if successful will further isolate Crimea and will allow the retaking of all of Kherson Oblast, as well as Zaporizhzhia Oblast, including Mariupol. While this would reestablish pre 2022 invasion territory, if you are Ukraine, how could you agree to stop there? You would have them on the run and the goal of reestablishing pre 2014 borders would be within site. Given the horror that the Ukrainian people have been subjected to, the human loss, and all the other sacrifices made, how could you justify stopping when you would be that close to total victory? I think you are correct in asserting that international pressure will be brought to bear to get this to stop at the point, if I am Ukrainian, I'm not listening. I'd press on as long as possible to reclaim what is rightly theirs.
I keep seeing where the Russian propagandist are saying that we (the west,and they specifically point out the US) are after the destruction of them and their culture. I'd argue that at this point, we should be after the destruction of their way of life. I can appreciate the artistry and ability of some of the things done in Russia, and I have no desire to have any of that destroyed. But in so far as the destruction of their elite Russian beliefs, I'm all for it. At this point, it seems this is a society in need of post ww2 German style humility, to the point of it being so humbling that the idea of creating an offensive force is blasphemy in their society. The only way this happens is with a complete dismantling of their current style of life and destruction of the propaganda machine that feeds it. For things to really change, a complete humiliation on a battlefield isn't enough, a complete dismantling of their current society is necessary. Otherwise, see you in a few years dealing with this same sort of crap, in Ukraine or somewhere else they think they can easily terrorize and get away with it.
How do we do this, I don't know. What I do know, is that if we stop at half measures on this, we will still have the same problem and be back at square one before you know it.