IMHO, a permanent ceasefire and peace may be established with neither Ukraine nor Russia losing face.

1. Each maintains sovereignty based upon pre-invasion borders with a permanent peace treaty in place.

2. Russia must pay war reparations for damages to Ukrainian infrastructure in exchange for lifted Russian sanctions.

3. Crimea is recognized by the United Nations as an independent neutral nation.

I think Crimea is the key. Imagine the prosperity of a free and independent Crimea. An East-West Switzerland or Monaco; open to trade with Russia, Ukraine, the Sea of Azov, and all the nations of the Black Sea, and the Mediterranean.

What are the chances?