Check Engine light just suddenly went off suddenly while driving, whats it mean? on 2001 Pontiac Grand Prix

It was on for a month or so and i was told it was probably a piston misfire and i needed to change the catalytic converter, so will it comeback on or just stay off till somthing else is wrong?

Asked by for the 2001 Pontiac Grand Prix
your car takes test on the whole vehicle at differnt times the light probably went off because what was making the light come on (failed test) must have passed the last test... it will most commonly come back on soon