That’s an interesting point. Very often after war regime changes usually end in disaster. That’s why treaties usually included indemnities to weaken but not destroy a rival. But would Europe be content to let Putin stay in power given the atrocities his forces have committed? I don’t think there’s an easy answer one way or the other.
Of course they would. They didn't have any issue when Assad used chemical weapons on his own people. Do you really think the UN is going to do anything? They are too busy formulating more condemnations against Israel, than N. Korea, China, Syria, and any Genocidal African regime combined.
We are giving NATO nations a shit ton of money, while they spend a ton on Russian oil. Secondly, we seem to be footing the bill when it comes to NATO, as they are not paying their fair share. I highly doubt any of them have the balls to do anything without the US being 100 percent committed to it happening.
If you remember, Bush, told his son, do not get rid of Saddam. Iraq was constantly at war with Iran, and getting rid of him created a huge vacuum which years later led to the creation of ISIS.
Assad, for all its worth, has kept his word with Israel. He did try the nuclear way, and Israel put an end to that very quickly with Operation Orchard in 2007. Of course Syria completely denies they had their Nuclear reactor bombed, but that is another story. Again, if Assad falls, the stability in that region becomes unpredictable, and you might have more than proxies do Syria and Iran's dirty work, which could trigger WWIII.
Libya is extremely unstable after Gaddafi. They have been under constant war since then.
Again, it is better to know your enemy, because the unknown could be disastrous as you have said. I just don't know of many scenarios where it hasn't been.