Phangan car-ferry traffic is small - 4 car-ferries a day, and that kind of passengers probably won't stop more than now by the pier to have somme food from market, if they stop there at all - most people heading for Phangan are foreign tourists using Lomprayah catamarans from Maenam and Bangrak, and Haad Rin Queen from Bangrak; Seatran Discovery has not yet restarted, but they also operates from Bangrak, i.e. Big Budhha Pier.
Tao-traffic from Samui is Lomprayah and Seatran Discovery.
If there comes a bridge it's likely that one of the car-ferry routes will cease operation - most likely Seatran, as it's private - the other route, Raja Ferry, operates from Lipa Noi Pier, south of Nathon...????