Unfortunately Russia needs to be broken. There was an uneasy acceptance of the 2014 annexation of lands. That was simply used as a launching off point for the current campaign.
There is no way to let them save face and nothing other than a full defeat can be trusted. At this point the wars in the main territory are only to hold on to Crimea and keep the fighting from the last warm water port for the Russian navy.
More than an embarrassment it would be a real and severe blow to the future of Russia for decades to centuries. Once the port falls, there will be no reason at all for Russia to care for Crimea.
This is even a bigger fuck up than it appears. Putin owns the biggest military failure since Germany invaded Russia.
All Putin had to do is put up a beach front villa in Crimea, trade with Europe and enjoy the ill-gotten gains of 2014. The western world would have accepted him with open arms. There is no victory to be won, only lesser losses to be groped at.