Originally Posted by corporate-wage-slave

Yes it does absolutely 101% happen and it's completely automatic. It even happens when BA cancel the service! Your next sector will not be available for check-in online or any other activity. Ditto at the gate, the whole show is stopped. The cancelled sectors can be reinstated, but you'll need an extremely good reason.

I once had a trip which was something like: NCL-LHR-HKG-MNL-SYD-AKL-CHC-HKK. The trip is a common one for me (I have Kiwi roots), so when fog cancelled the NCL-LHR sector I knew what was to happen. I took the train to London and then on to Heathrow, I was at LHR 3 hours before the HKG departure flight. I spent 2 hour 20 minutes as the staff desperately tried to reinstate all those sectors, which were on waitlist to other passengers. In the end I just made the HKG service, and had another 2 hours at HKG your trying to get the rest of the outbound together. It took many many phone calls to sort out the return leg too.