Yes, that's a general point that there is now very little point going to an airport if your service is cancelled (as opposed to delayed), there isn't a lot that they can do unless there is another flight with seats that still makes the connection. Obviously one should try to get to the Contact Centre if possible. Unfortunately MMB won't give that option (to delete a sector). If the flight is badly delayed, won't make the connection but the train will, then you best call since you need to avoid being a no-show on sector 1. I once encountered someone who got into T5 before they no-showed on their NCL to LHR flight, took a very early train service in other words, so the computers aren't that clever. But then when it came to boarding their longhaul there was an almightly mess at the gate since the ticket said one thing and Ready to Fly said the opposite.