Russia will probably carpet bomb or thermobaric bomb it...The fighting in the Azovstal plant is going to be brutal.
If I was Russia, I would blockade it and let them starve and die. There is no use in entering that meat-grinder and wasting Russian lives
Patience...I mean they kind already did threaten war at the start of the operation if they gave weapons to Ukraine, but their bluff got called. If Russia wants to prevent this, I think they could bomb the rails on the Ukraine side, when the front of the train is officially on the Ukraine border. Then wait for the train to stop, then bomb the front train to keep that railway clogged, keep watch of the spot and bomb again if they attempt to fix it