Countries
US
The biggest, if not only, winner of the event. The only one who wishes the event to happen, so that money can go back to US from EU (due to regional instability) to reduce the high inflation in US.
The only loss would be the confidence of US's allies accounting on its support.
If Russia does not invade Ukraine, NATO will be dancing at its doorstep which is super preferable to EU and US, but intolerable as to Russia.
If Russia invades Ukraine, EU and Russia will be against each other by sharing a military border, so that US (and UK) will have much less to worry about on these two opponents.
Russia
Has no advantage but military strength, has no means of diplomacy but threatening, has no choice but war. Pity.
European Union
Realize the event too late. Cannot do much. Now that Ukraine is under war, EU is bonded to US once more.
Ukraine
Stupid as fk. Lost everything because of some vague promise by US. Let war happen on its own soil due to some stupid and irresponsible politician breaching the status quo.
China
Cannot do anything. Cannot blame Ukraine as it's the victim. Cannot blame Russia since they are to some degree allies against US. Cannot defend Russia since Ukraine’s sovereign is threatened as a fact. Can blame US but few would listen, and the plot is just too good to believe.
Similar Event in History
Philippine on South China Sea
Stayed calm. Knows its position and is smart enough to avoid being used as pawns of US against China. US did not get anything but swear from Duterte to Obama.
Japan on Fishing Island
Japanese forced to lose its ground. US succeeded to break down the free trading pact between China and Japan.
South Korea on THAAD
Korea was forced to lose its ground. US succeeded to break down the free trading pact between China and South Korea.
Ukraine’s Only Options
Ukraine could be independent as North Korea if it did not give up its nuclear arsenal. Could be stable as Taiwan if it did not join any sides between NATO and Russia.
People
Zelenskyy
He is the main one accountable for this event due to lack of insight in foreign affairs and diplomacy status quo. He is not smart enough and has too much goodwill as the leader of a weak nation. He is bound to fail just as Allende in Chile.
If he dies he will become martyr of Ukraine Nationalism and neo-Nazism (ironically as a Jewish), and as an iron proof of Russia invasion. This is the last thing Russia would like to see, but the best thing US wants to see.
If he flees to US without public announcement he would probably be killed by US to fake the previous scenario.
If he flees to US with a public announcement, Ukraine Nationalism would suffer such a hit that Ukraine may just disappear as a country forever. The best thing Russia wants to see.
If he stays and is still the president after the Russian invasion, he will be a National traitor that sell his country to Russia.
In other words, his 'friends' wish he dies and his 'enemies' wish he lives.
Putin
He is what he is. He knows what Russia is good at and is not afraid to use its force when necessary. But honestly, he has no choice.
US Politicians
Still so good at manipulating the world.