From every stand point of view,

it's to stop the war as soon as possible.

So may be is best idea is to divide Ukraine to WEST Ukraine and EAST Ukraine and this will take Putin's excuse for war away.

also refer:
- Czechoslovakia! to stop war, they divide to two country: Czech and Slovakia.

- Sudan: to stop war, they divide to two country: North Sudan and South Sudan.

- Yugoslavia ... and more

And when time is ready they can reunion like east/west German