>loss
How can you lose something you never owned to begin with?
Ukraine is, since around 2010, in flux between Russia and the west, leaning a bit west since 2014.
As for what happens with advisers in such scenarios, guess the same deal as in the Georgia war. They get evacuated.
It's not a "just because" fight. Syria and Libya were way worse cases of that.
This is about maintaining the US alliance network in Europe, which however under-militarized and acting stupidly at times (not without US influence there), still has some of the more advanced armies and military technology on the planet. If Russia throws its weight around in Central Europe and USA ignores it, that raises questions about what's the point of NATO. Probably would be great news for the French, if they are smart they may even turn the leftovers into a mini-NATO, capture some of the political infrastructure, provide replacement nuclear umbrella, and in exchange get allied support for their adventures in ex-colonial Africa and a lot of prestige they love.
Also how is it turning everyone else against USA? Its not like Russian expansionism is loved in the region, quite the opposite.
In the end, the way "based" Russia pacified Chechenya for good was to send big bags of money to a local warlord to do it for them. And the deal is that they have to keep sending them, and not ask questions how he does it or where the money goes. If they stopped, trouble would start faster than an election cycle goes.
Here's the problem though, Ukraine is many times bigger than Chechenya. Russia is not America, it cannot afford to spend trillions USD on a 20 year peacekeeping and rebuilding operation. It would drive them bankrupt. They already are thin on cash, and they would get hit with sanctions on top of it. So the trick is for the west to simply arrange it so that the occupation is costly to Russia, in money and PR terms, they don't have much reserve in either. Their tip of the spear forces get stuck in Ukraine for good, demoralized and possibly suffering attrition from the unpleasantness of COIN warfare, military and rebuilding budget doing whatever possible, while its still 30-60% short of what is needed. At the price of Ukraine, which 2 decades ago Russia still solidly ruled by proxy, Russian conventional military is practically neutralized in regard to threatening other countries in the region with similar actions, because they can't let go of Ukraine, yet they also can't afford the investment to make it self-sustaining.
That would be a strategic victory for NATO.