[DaRk_RaiN]

You have to use OnPlayerUpdate to check if he's still in the area

pawn Код:

OnPlayerUpdate(playerid)
{
if(!IsPlayerInArea(playerid, Float:MinX, Float:MinY, Float:MaxX, Float:MaxY) && Capturing[playerid] == 1 )//the coords of the gang zone
{
KillTimer(SetZone);//The timer that will set the zone ect..
SendClientMessage(playerid,-1,"You fail to capture the zone Don't leave the area!");
}
return 1;
}

Note:You need to make a variable to detect that the player has started a gang war, its should start when the players enters the CP and stps when he leaves it, else it will be bugged