It doesn't specifically answer your question, but I think it pays to come prepared regardless of what you think the airline might do.

For me, that means carrying a Thermarest sleeping pad in my luggage and a flannel sleeping bag. It also means a membership to your elite club of choice. Then you're assured some comfort if things fall apart.

If the flight is delayed you will be put on another flight and you will probably be in a position to request your original routing, or to request miles that correspond to your original routing.

It can get hairier if you're dealing with nested tickets or itineraries where one MR depends on another. On the first leg of my very first MR, my flight was canceled due to mechanicals, which totally screwed me up because I had a nested ticket on the same airline. The manager who was sent to re-book us, god bless her, fixed not only my immediate run, but the nested ticket that was affected by my re-route.

In any case, being extremely nice and extremely appreciative for whatever courtesy they can offer you will pay off. If you leave prepared, even an overnight delay will just seem like part of the great adventure.

-KF