I believe the voted off castaway is at the mercy of the show's sponsors:1) Tandem base jump from the falls with a target parachute with the Target logo. The chute would be lit from underneath using a halogen helmet mounted flashlight. Very dramatic.
2) A beer sponsor (Bud Light) would have a keg-shaped barrel. This would tie in with a revival of 'I asked for a BUD liiiiigggghhttt." commercials
3) (and possibly realistically) They could have the person rappell down the falls. Burnett has a lot of experience at having rope courses on and near falls set up for his Ecochallenge, including nighttime descents. That would add an element of fear to being voted off.