If you are going Standby on a flight, Revenue or Non-Revenue.
NEVER walk away from the gate until the airplane is gone, left the gate, moving.
So many times, I was able to get someone on at the last minute. Door is shut, flight monitor says flight closed. NEVER walk away until the airplane is moving.
Over my many years working flights and going standby, I have seen it, the ones that do not leave might get on. You never know, customers get off, there was an empty seat, a maintenance delay, so many things can happen. Stick around till you see the flight depart and is moving.