[Micah]

No, the spell is cast first, then the attack happens. Low-level horror attacks also don't pose much of a threat to a prepared mage. Astral mages can cast returning, naure mages can spam a couple of swarms, death mages can skel-spam and follow up with drain life, fire, water, and air all have direct attack spells that will kill a horror as long as it gets stuck on bodyguards for a few rounds. Blood has leech and life for a life. Earth lacks anything stellar to deal with them, but that's a pretty small segment of the mage population.

Every so often you'll get unlucky, or something really big and nasty will show up, but there are plenty of ways around it.