Even if Russia were to withdraw to pre-war borders, Ukraine would keep fighting because they insist on taking Crimea which is a large majority Russians who want to be part of Russia.

Crimea has never truly been Ukrainian. It was internally transferred to the Ukrainian SSR in the 1950s, but its population was Russian then and stayed Russian the whole time since. But Ukraine insists on having it back.

And if they did somehow get it back, they would start ethnically cleansing it of Russians. I hope you understand how that’s a bad thing.