In unlikely the event of being taken down by someone that have basic groundfighting skills it will really hard for you to use biting och eye gouging.
At least that would be an option that is on the table. I've seen many MMA fights where they are on the ground and the person's arm or hand is right by the other guys face, but obviously they can't bite or poke at the eyes. But in a real fight you could if the opportunity arose. I agree that if you are mounted and getting pummeled with punches, then biting would probably not be effective at that point.