I think they make the cancellations before any connections can board their flights, at least from the QR experience:

"Australian family Emma Young, her husband and their two daughters Amelia, three and Georgia, eight months, booked to return to Brisbane immediately new flights became available on Qatar Airlines several months ago and they gave notice on their London property and sorted accommodation in Brisbane.

As late as Sunday their seats were confirmed, but yesterday they received a call from Qatar Airlines, bumping them off its just over a day’s notice and without any offer of a possible alternative flight.

By the time they received the call, the family had already had had their furniture collected by removalists, and their two cats had been picked up and are now en route to Australia on a cargo flight. When The Australian contacted them in the hour before they were being made homeless the family was desperately calling airlines, sitting on a small blow up air bed in the empty lounge room.

“I just don’t know what we will do if we can’t get on the flight, we are out of the house as of lunchtime and have booked a hotel room for tonight, but then what do we do?’’, Mrs Young said."

https://www.theaustralian.com.au/wor...4f234d42235f2f