1. Commit their tanks to combat against the Russians. Th is, IMO, "stand and die"
2. Destroy the tanks in place, pull out their troops, fight an unconventional, asymmetric war.
3. Pull troops and armor back across the Ukraine. Trade land for time...see what develops.
That's really all there is. None are great..However, from, best to worst options, in order, it's last to first..