Assuming the regime falls and leaves a power vacuum, what do you think the best way to help the people toward that is?

My greatest concern is what comes next. The current regime is a kleptocracy, which is awful for the people, but easy to predict and control and siphon cheap natural resources from. They stay in power partly by fear of EU/NATO, but it’s questionable support. Once the kleptocracy is gone, EU/NATO can either embrace Russia or maintain the current stance against them. Embracing Russia will diminish EU/NATO power and purpose. Maintaining the current stance will strengthen the alliance against them, while pushing the country toward extreme nationalism in a new regime with nothing to lose and a lot to prove. There will not be a clear decision point to switch course; it will either be gradual de-escalation on both sides, or gradual strengthening.

That sounds like a super hard problem, because USSR already collapsed once, and stuff seemed like it was going to a better direction, but in the end we got Putin. Also, it's in interests of China to keep a some kind of power balance, so at least I think that EU/NATO shouldn't think the fate of Russia as "not my problem", or else China might do some opportunistic power plays.

Oh, let's have some other examples: Japan is doing great these days. I cannot help but think that the American occupation was beneficial for the country. (To be sure, I'm NOT arguing that the nuclear weapons were warranted.)

On the other hand, Afganistan yielded to Taliban right away as the US forces retreated. So clearly your mileage may vary with interventions!