So if they close off the mine and fortify their flanks, they can hold out and kill a lot more russian meat being thrown at them until they need to retreat those good troops a bit further back, where they can continue the fight.

I don't think russia will be able to maintain the pressure for long enough, until they need to start drawing children and the pressure in kremlin starts to rise. Play the long game and make them pay heavily for every cm they get. And when they have it, come back with better NATO equipment and trained soldiers