If I were the Ukrainians I would be coordinating my military defense with Latvia, Lithuania, Estonia, Poland, Bulgaria, & Romania. As a group they could stand up to the Soviets. Otherwise it will be hang divided. This crap is going to get real grim real fast.
The problem is that the Ukrainian military is divided. There are many Soviet holdouts loyal to Russia within itself. Many of those units will desert and join forces with the Soviets.
Moving into Ukraine would be pushing it for russia...the Euroweenies are going to start swallowing Valium instead of Gummi bears!