Ukraine is not in NATO. And I'm afraid if NATO and EU have to choose between a direct military confrontation of nuclear-capable powers and a genocide of 40-million-and-dwidling Ukrainian population, they'd choose the latter as long as Putin keeps this contained in Ukraine.
Would it turn Russia into Greater North Korea? Absolutely. Would it cause outrage and grave concern? You bet. Would it make NATO to move in and stop it? Unlikely at the moment.
But in Europe that outrage will also be from a place of fear: maybe Russia will do it to you, too. So it will be longer lasting and a more intense and probably a truer feeling. Not fake outrage.
And even if it were, no NATO member will set foot in Ukraine while this war and the following insurgency are happening.
What will happen is, depending on how hard Putin pushes, the reaction will be just as strong. More attacks targeting civilians? More weapons sent to Ukraine. Harder sanctions, with actual teeth. I wouldn't be shocked if by next winter 60%+ of the gas supply for Western Europe will be covered from other vendors, more or less bankrupting Russia (a huge percentage of Russian exports are raw materials, primarily oil and gas).
you will be shocked to discover that Russia is going to fuel China's economy instead [1]
[1] https://www.bloomberg.com/news/articles/2022-02-28/gazprom-p...
And the sanctions Russia is under will be nothing like the ones that will be heaped on top.
Europe is highly sensitive about local conflicts, especially after what happened to Srebrenica. Grozny didn't really count since it was:
a) an internal war
b) at the end of Europe
If Putin flattens a major European city (for Europe any city above ~2m or so is major), the outrage in Europe will be huge. Even bigger than it is now.