With my flight from Paris to San Francisco postponed until tomorrow to fix a mechanical problem, I have been pondering the logistical problems that such a delay creates. The scheduled departure was 1040, but we didn't board until nearly noon and finally deplaned around 1400. During that time, I can only assume the machinery for handling the potential (which came to be actual) need to rebook or otherwise accommodate passengers is put into motion early on. When there is a delay and the potential for a serious problem, I imagine hotels that airlines have on some sort of contingency are notified and contacted to see how many rooms are available. After all, it's not like the airport Hilton is going to have 400 empty rooms. (It's also possible only us superior mileage status uber-humans get to stay in the Hilton while the proletariat stay elsewhere).
Booking people to stay overnight is one thing, but rescheduling is another. I imagine most of us will be on the flight tomorrow. For the few who had an urgent need to travel, their rebooking options were probably very limited. We didn't deplane until 1400 and most did not reach the counter for assistance until 1500 or 1600 given the long line. By that time in the day, most Stateside-bound flights form Europe have already left. Going west is a day flight. Only going east, especially from the West Coast is it an overnight flight. Even if you manage to get another booking, your luggage is not going with you. For the record, almost all checked bags have been left on the plane and will be there when we (hopefully) fly tomorrow. Finding a handful of specific suitcases in a cargo hold of nearly 1000 bags would take a few hours. More likely than not, even if you actually made your way onto another flight, your bags would still arrive with your original plane.
Then there is the plane problem. Not our flight, because we get the same plane for tomorrow. The problem is this is a CDG-SFO non-stop that flies every day of the week. This plane needs to be in San Francisco later today so it can be turned around and flown back. (There are a minimum of two planes to sustain this rotation since one needs to fly each direction each day and it's too long for a single plane to make the round-trip). The question becomes, how do the people who were planning to fly from SFO to CDG today now get where they are going? It's not like spare 747s are lying around and certainly not at a non-hub for Air France like SFO. No one is going to say, "Oh looky here, we found one that fell behind the storage locker" unless it is the storage locker that holds this. In fact, I was flipping through the Air France magazine and they only have ten 747s and five Airbus A380s in their fleet (and Wikipedia claims even fewer with eight and four respectively). Regardless, these are all planes that probably fly or have some predetermined schedule well in advance. That's part of why we didn't move to a different plane here. This is their hub and there wasn't an available 747. The SFO-to-CDG group did have more time to try and rebook people, but this is 400+ people who all of a sudden need a new plan.
I can only assume airlines, and Air France in this case, have contingency plans and have largely planned for these types of scenarios in advance. It should be standard exercise for them to find a plane, repair a problem, rebook passengers, get hotels, etc. These are all high-probability needs, not on any given day, but given volume and time, these plans will need to be used. In the same way, I assume the U.S. military has "contingency" plans for an invasion of Canada. You don't want to ever use it, but stuff happens and then your hand gets forced. So Canada, you've been warned!