Ukraine had a far more favorable peace treaty at play in march of 2022 than they ever could get now. The treaty wasn't sunk by Putin but by the intervention of Boris Johnson who promised unconditional support for Ukraine ad infinitum. If Ukraine desires to exist as even a nominally independent country, they will take the next treaty offered without any complaints. Otherwise, they are not in a position to decide the fate of the nation, assuming that even remains as an option considering future relations between DC and Moscow. If you desire a past example, you can see that in south Vietnam.