problem is if it is the bearing it can potentially seize and your car wont drive. you will be stranded on the side of the road. there is no real set time on when this will happen, it just will....eventually

 

you are fine to drive. if it were bad the noise would be very obvious.

i would say that morelikely than the alt it is the idler/tensoiner pully. in my expirience not counting the s, they go bad a lot more.

the idler pully is the one that doesn't do anything.

 

i suggest fixing it and not takin the risk, its at your disgression.

 

Remove the belt and start it up, a short run will not hurt.

 

Remove the belt.

spin all pulleys by hand, wiggle them, whatnot. Loose or freeplay=bad.
Grinding kinda inside, or catching when you turn them = bad.

inspect the entire contact surface of the pulley, it should be pretty smooth and not out of round.