[FailerZ]

If I understand:
You need to make a variable like

PHP код:

//On top
new bool:IsAmbLoaded[MAX_VEHICLES]; 


Once you load the ambulance in your script set it to true with

PHP код:

IsAmbLoaded[vehicleid] = true; //The vehicleid is the ambulance 


and do the check onvehicledeath like

PHP код:

public OnVehicleDeath(vehicleid, killerid) 
{ 
    if(GetVehicleModel(vehicleid) == 416 && IsAmbLoaded[vehicleid] == true) 
    { 
        //Mission failed
        IsAmbLoaded[vehicleid] = false; //Don't forget to reset the var to false after the mission end 
    } 
}