Should the event transpire, I'm quite convinced that even in our reduced state, air superiority and soon following, USAF air supremacy would prevail over the Ukrainian skies.
The Russians have never been tested and don't really know what they are doing. Their command and control doctrine is archaic, they have little real-time experience, and in a confrontation with USAF would be toyed with.
The big if is which side the US administration would be on.