Jesus, make sure this serious conversation doesn't happen again. ...and 1 - absolutely no machinists! That strategy won't work against mages! Goblins will take care of them...
2 - maximize magic resistance; they don't have any overwhelming magic, which is a big disadvantage, by the way. Of course, there's Jesus's staff, but it's not guaranteed to appear in the shop.
3 - try to rush the mage so he doesn't cast too many spells.
4 - if the game drags on, there might be problems.
But he's right about that; mages can still manage to win.