Shock to a magnet can affect the stability of the magnetic field. Also depending on the type of surface the magnet would be hitting such as steel or wood. A magnet hitting steel would do more damage to the magnets field than the surface of the wood. I've tapped a bar magnet on a steel rod and magnetized the rod. This can change the alignment of the magnetic field within the bar magnet. Damage to the coil might occur if it hits another object. Dropping a pickup could cause the coil to get gouged or dented and breakage of the magnet wire.
WRITTEN ON JUNE 12, 2015, BY