A good example of an effective peace treaty was the Camp David accords that put an end to the Yom Kippur war of 1973. That used interest based bargaining instead of distributive bargaining.
The outcome that Russia is interested in this conflict is:
- annexing territory (Crimea, Donetsk, Luhansk, etc)
- help Ukraine facilitate the international recognition of that annexation
- Ukraine should not join NATO (this makes another invasion viable in the future)
In this deal, Ukraine gets:
- a ceasefire
- some peacekeeping help
These terms are pretty mediocre for Ukraine. This administration seems to be inclined to think that's the best Ukraine can get and they should take the offer to prevent further losses.
Oblasts like Crimea, Donetsk, Luhansk, etc. have a high percentage of ethnic Russians living there. That would remain a barrier for Ukraine to achieve peace even if Russians retreat to pre-2014 borders. Nobody knows exactly what percentage of Russians live there because the last census was long time ago.