So we have to find out what secrets they are protecting? Can we move them, get them out, destroy them?
It seems, lending them a hand until they decide they must flee is still better then not going at all. They have said they will stay. They are showing they will stay and die to the last. We can go and give them a least a little strength maybe saving at least one mage maybe not, but we will also be deflating the enemy even if just by a few.
If 'the blood of innocents is not on our hands' anyways, then helping them fight may give give them hope, but that means they will fight that much better before they die. Grim out look yes, but....