While I wasn't actually on the flight, when I worked for American in Seattle, we once sent an MD-11 to Tokyo with only one non-rev passenger on the flight.

The flight originally was booked almost full, but a maintenance issue was found that looked like it would cancel the flight. Only after the agents rebooked all the passengers on other flights/airlines, maintenance resolved the issue much sooner then expected, and since the crew was still legal, they sent the plane out with a full belly of cargo, and one passenger.