Flags from decompiled scripts:
0 = normal exit and closes door.
1 = normal exit and closes door.
16 = teleports outside, door kept closed. (This flag does not seem to work for the front seats in buses, NPCs continue to exit normally)
64 = normal exit and closes door, maybe a bit slower animation than 0.
256 = normal exit but does not close the door.
4160 = ped is throwing himself out, even when the vehicle is still.
262144 = ped moves to passenger seat first, then exits normally
Others to be tried out: 320, 512, 131072.
This is the server-side RPC native equivalent of the client native TASK_LEAVE_VEHICLE.