Once the brake pad wear indicator goes of, the sensor will have to be replaced. That is simply how they were designed. If you had noticed the pads were wearing down and had replaced them before the light went off, you would have been fine. Replacing the sensors is easy. Unplug old. Plug new ones in.
Um, now that I think about it, you may have to remove the brakes to wedged the sensor in with the pad.
If you are responsible enough to keep an eye on your brake pad wear and you don't mind having teh light on your dashboard, it may just be better to leave everything as is and just replace the sensors the next time you replace the brake pads.
Otherwise, you will need to remove the brake pads that have the sensor attached to them -- one in the front, one in the back, but I don't know which side it would be for your car.
Best of luck.