As we saw with Saddam and Gaddafi, removing the head of the beast just creates a power vacuum and gets the different factions fighting with each other for control - that really would be a bad thing for Russia and the rest of Europe.
I agree to that, as such, my suggestion to break up the Russian Federation in its individual states, which each do have a kind of "local government" already in place. Of course, a lot needs to be done, though, replacing Putin with just another dictator in a huge country, isn't going to take away the Russian threat, given its population seriously believes in all what the propaganda said. You're not going to change that in just a few years. So, better have a lot of small countries, who initially do not want to "work" together, etc, though learn on that, and each in itself aren't a threat to NATO.
Also, these individual states no longer have the ability to pay for the Nukes, so, these will also get scrapped.
Just assuming, it is possible to "bring" a democracy isn't something that is going to work, recent history has shown this extensively.
Having a lot of smaller though independent countries, condemned to gradually start working together to accomplish something, along the EU model, is one of the very few options, I think, to get rid of the Russian threat.
And, the above also sends a serious message to China, what might happen, in case they think a Hitler game would be appropriate.