It's not a difficult issue, and some carriers are better at it than others, it seems. But in any event, it should be all worked out in advance and on the shelf in a manual in ops control ready to be taken down.
The fact it happened on a Saturday afternoon rather than a weekday is illustrative of modern trends, despite it being a 24x7 industry, where nobody low enough in the hierarchy to be working the 24x7 shifts, rather than office hours, is allowed to decide anything.
A realistic plan would have AF cancel the first (or first two) evening departures from Eastern US/Canada, and send the aircraft to Goose, which would allow the crews enough hours remaining to transfer the passengers and take them on to somewhere more hospitable, if not LAX then at least a major city with hotels and onward flights.