Unless BA is fully at fault, the remaining sectors will be cancelled and you can't count of them being reinstated. I had a flight a few years ago from NCL to New Zealand, there was fog on the Tyne, all NCL services cancelled. I took the train instead, got to LHR well before my HKG flight was due to depart (2 hours? maybe more) and yet it was touch and go as to whether BA could reinstate the HKG service in time for my departure, and each remaining sector required considerable effort to get reinstated. All seat reservations lost along the way.