So it's another Munich Agreement, then is it, Neville?
C'mon, Brother! You're a descendant of William the Conqueror, possibly, or perhaps a fan of George Washington. Even George had his challenges as a new commander, including a surrender and demotion in early Pennsylvania. These things do take time. Consider if some wackos laid claim to the area from Bristol to Cornwall, or Charleston to Baton Rouge. No fight? The US would lose its best Bar-B-Q and strip joints, the UK its best seafood and pasties. Unacceptable! Ha, ha. That's what Ukraine is facing.
The nationalistic warmongering is coming from Moscow. Determined backbone is simply what they've met, and didn't expect. Putin is crumbling.
Finland has joined NATO. The center of gravity in European backbone has shifted to Warsaw. Russia's "allies" from Minsk to Tashkent want nothing to do with him. Russia runs scared of its own "Victory Day" celebrations today (09 May). Putin will fall, though it may take time, even a decade.
That said, your point is right. Ukraine's time is now. "As long as it takes" is a friend's slogan. Ukraine has no time. This is Yorktown. Cornwallis is in George Washington's sights. Foreign allies have joined the fight. The time to close it is now.
The "what", you mention, is for Putin to fail in his land-grab. That's doesn't mean all land vacated immediately. Like Transnistria in Moldova or Abkhazia in Georgia, that may take a decade. It does mean Putin negotiating in weakness. Clamoring to save face. Propping up the economy. Pandering to the Chinese. A Kim Jung Un of ridiculousness and servitude. His authority shriveling, over time, like a cheap Matryoshka doll, and finally to nothing. The rest of the world moving on.
Those around him will take care of the rest.