edit: I get that this sound snarky, but it will hopefully drive home the point. Unless you have a 3rd alternative to agreeing what ever the man with the nukes understands under "demilitarization and denazification" and joining a death cult with mandatory membership i dont really get what i can tell you.
For Russia to leave them alone, and however it takes. Russia's economy is falling apart, and their army is in brutally terrible shape. They couldn't possibly occupy the country, even if they manage to conquer it, which they don't seem to be able to do. So victory for Ukraine is certain, ultimately. It will take time and cost a lot of blood and destruction, but the alternative isn't great either - being subjugated by a brutal tyrant who has no qualms murdering those who oppose him isn't a walk in the park either.
They are the ones choosing to fight. Look at the polls. Look at the interviews. Look at all the people there voluntarily picking up arms to defend their country.
Russians, not Ukrainians.
Ukrainians will defend their country and the Russians won't have the stomach for a prolonged insurgency, just like in Afghanistan.
Afghanistan led to the fall of the USSR, and Ukraine will now lead to the fall and breakup of Russia.
What ever solution you propose will have a cost in Ukrainian lives and that cost is largely determined with what Russia is willing to do. With their ruthlessness reducing their casualties massively.