Usually pilots wait 5 minutes,right?Once I had 5 passengers missing and since pilot knew he could land on time,he delayed 15 minutes.Guy landed 20 minutes earlier too.
normally the rule is if the passenger has a boarding pass on that flight the ground staff has to find him or her from inside the airport. because flights cant leave passengers behind. that's the rule. As i have seen lots of ground staff coming to the waiting areas and screaming on top of their voices by the passengers name. and there he is seated there like he does not know what's happening. most of these things happen when the passenger does not know English bcos airports most of the time announces in English. Lots of indians don't understand so they just sit on the ground and enjoy the view out side. but the last decision is with the pilot. he can wait for 10 or 15 min if no pax is there he can leave.