[Carlton]

It takes a delay for users to exit the vehicle so you would have to start a timer and make them re-enter it.

pawn Код:

new MyVehicle[MAX_PLAYERS];

public OnPlayerStateChange(playerid, newstate, oldstate) {
     if(newstate == PLAYER_STATE_DRIVER) MyVehicle[playerid] = GetPlayerVehicleID(playerid);
     return 1;
}

public OnPlayerExitVehicle(playerid, vehicle) {
     // SendClientMessage(playerid, 0xFFFFFFFF, "You can't exit >:]");
     SetTimerEx("PlacePlayerBackInVehicle", 5000, 0, "i", playerid);
     return 1;
}

forward PlacePlayerBackInVehicle(playerid);
public PlacePlayerBackInVehicle(playerid) {
     PutPlayerInVehicle(playerid, MyVehicle[playerid], 0);
     return 1;
}

I just coded this at the spot, so if you find any bugs, post it.

Edit: There's no function to force a player to stay in the vehicle.