First thing you might want to check is your wiring in the bass guitar. Check for broken wires, loose connections, especially by the pots (volume, tone knobs) and the jack. Another problem to look for is called a Cold Solder Joint. This is where a wire looks like it is soldered, but really it is loose and doesn't have a proper contact.
Check those out first, because generally (not all cases) a pickup doesn't fail like that very often.
And like previously mentioned in this thread.... check the bottom of the pickup and see if the magnet fell off. Might be just a matter of reglueing....