Putin Goners doesn't guarantee Russian mentality to be goners, he's most likely a symptom of it, a part of the post-KGB spiderweb that has the real power in Russia. Removing a leader (which can mean anything from retirement to public killing) after he lost (or even "didn't win") a war might lead to leaders that are better at winning wars, not necessarily not starting them.
Remember that Putin was absolutely fine playing the economic game for years, and only now "suprised" half the EU by starting a war of barbaric conquest. Studying why he found it necessary to abandon the clearly superior diplomatic route that gave him money and influence over the EU in order to start fighting Ukraine might be a key here. Not just to figuring out Putins next moves but the mentality of the Russian state as a whole.
Status quo would also be a mistake. We just simply cannot expect to tell Russia what to do and expect it to happen long term.
I obviously do not have the answe, but repeating the treaty of versailles would be a grave mistake, as would the "help" Russia received in the 90's from the West.
They're obviously stuck in their "Russia STRONK WW2 WINNER YAY" mentality, which serves no purpose whatsoever. The fact that their leaders are a product of the cold war does not help either. Putin and his gang is clearly not the ones anyone would negotiate with, but in the end it would be useless without China onboard aswell.

There already is a form of civil unrest. Pretty much every day there's someone new declared a "foreign agent" due to their actions. Just recently Alla Pugacheva demanded that she be declared one after her husband Maxim Galkin was due to his condemnation of the war (and she herself called out sending our people to die for illusory goals in her post). She is a woman about whom the joke "Leonid Brezhnev (or other politician) is a minor political figure from the era of Alla Pugacheva" was made, so we shall see how Putin measures up to her stature.
Just an aside, but Ivan IV's epithet of "Grozny" being translated as "the Terrible" is an incredible misunderstanding of its true meaning. It literally means "of the Thunderstorm" and means more "awesome", "great", "just", or "God's judge on Earth" (during his time those who dies due to a lightning strike were seen as saints). It also wasn't applied to him until after he dies and became a subject of folk songs.
Terrible in it's more archaic usage as a play on nicknames of past rulers holds a meaning closer to the word powerful in modern English, that one feels kinda sketchy for a man that will have served to stunt Russia for decades from what it could've been.
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I wouldn't say it's a huge mistranslation so much as that the meaning of the word has just shifted. It used to be a lot closer to the Russian meaning than it is now.
"There is a pervasive myth that making content hard will induce players to rise to the occasion. We find the opposite." -- Ghostcrawler
"The bit about hardcore players not always caring about the long term interests of the game is spot on." -- Ghostcrawler
"Do you want a game with no casuals so about 500 players?"

While Japan proper were never invaded forcefully, the allies did occupy it in it's entirety after the Japanese capitulation for a few years.
That rehabilitation happened because the US were actually in a position to force the systemic changes necessary to their society at a core level. It's not comparable to what an eventual Russian defeat could ever realistically lead to.
"There is a pervasive myth that making content hard will induce players to rise to the occasion. We find the opposite." -- Ghostcrawler
"The bit about hardcore players not always caring about the long term interests of the game is spot on." -- Ghostcrawler
"Do you want a game with no casuals so about 500 players?"
I say it was somewhat less successful because with Germany they were very successful in removing nationalism. Not at all with Japan. Germany is deeply ashamed of the war crimes it committed. Japan refuses they ever happened. Which was inevitable; you cannot try and convince people to acknowledge their war crimes after wiping out two cities of the map and leaving behind a legacy of misery.
I'm not surprised by this, words change over time and meaning can vary, even between closely related languages. Take Stout for example, in Dutch it means naughty, in English it means strong, among other things. So a mistranslation is very likely.
As for the social unrest I just read that the Duma is proposing a new law making it illegal to refuse to fight, punishable by up to 10 years in prison. I'm sure that will quell the unrest.

I think people are overestimating the resources required to modernize Russia. Neither Germany nor Japan had the prerequisites to become an egalitarian country. By contrast, Russia has political opposition, however weak it is currently due to censorship, and a receptive audience.
What most of the polls from which you draw the conclusion that "76% of Russians support the war" don't tell you is that the support is mostly concentrated among the old people who are on their natural way out. The younger you go, the less this war is supported, with pretty much even split on the support among 20-35 years old bracket (in a poll conducted in a non-free country, mind). After our government tried to teach "patriotism" in schools every Monday, the teachers collectively decided to teach something else instead, and children collectively decided to miss these "Lessons about the most important".
The younger generation of Russians is mostly culturally European. They don't want this war, they don't want the return of USSR or Imperial Russia, they want to be free and enjoy their lives. It would be a great misjudgment on the part of EU and the US not to seize this momentum and instead allow this generation to be lost over some old people's revanchist grudges.