Bottoming out the driver can cause damage but that doesn't mean it necessarily will. Run some sine wave test tones on it, like 30 hz, 40 hz, 50 hz, if you don't hear anything strange it is probably ok. Your subwoofer is probably fine, you just don't want that to bottom it out a lot. Bottoming out is when the voice coil hits the rear plate, and if it hits the rear plate enough, it can hammer it out of shape, and then your driver is ruined. By the way, don't run the sine wave test tones at loud levels for prolonged periods of time, sine waves are hard on drivers, it will heat up your sub in a hurry.