Don’t get cocky, everyone. Remember nuclear warfare has been flirted with.
I don’t think there’s much that can be done for Russia using nuclear missiles on their own territory and that would be why Ukraine’s in an area of value, protecting them from that happening. They won’t be controlling territory much larger while an Su-35 with a nuclear loadout is waiting for them to stray enough kilometres away from the critical infrastructure.
Consider it a siege attempt on resource, not a counter attack for territory.