Putin will have a bit of trouble rigging an election in the Oblast that controls the land approaches to Crimea with only 14% Russian population.
The Chinese would be very happy to pay Putin for control of such a fine commercial port as Odessa. Odessa could also be used to supply North American LNG to Ukraine and Europe.
The oblasts along the Sea of Azov aren’t heavility Russian, but they’re no hotbeds for Ukrainian nationalism, either. I will be very surprised if Kiev retains anything east of the Dnieper River by the time this whole thing plays out. Putin will find a way to take what he wants, and it doesn’t look like Ukraine has the ability to stop it from happening.