Heh.....it happened to me back in 2004 when I was flying ORD-ATL-LGA.....with the ATL-LGA flight being the 2nd to the last of the day (8:30PM departure)
My departure from ORD was delayed due to weather and even though the GA tried to switch me over to a direct flight on another airline (she made a few calls...but it was Labor Day) and eventually "protected" me on the last flight from ATL-LGA, it looked very likely that I would be stranded in ATL overnight (something that has never happened to me at any airport......even to this date).
IIRC, my flight finally departed ORD with a scheduled arrival time in ATL of about 9PM.....which meant that I might get a seat on the "protected" flight.
However, ATC delayed my flight enroute by an additional 30 minutes and we finally got to the gate at 9:30PM.
As soon as I got off, I asked the agent meeting the plane about the status of the flight that I was "protected on"....and learned that it had just left.
However, the agent pointed across the walkway to an ATL-LGA flight that had been "held for connecting passengers"....and sure enough, it was my original 8:30PM flight (DL1736)!
To say that I was surprised to learn that its departure was initially delayed by 1 hour...and then shocked to see that it was being delayed an additional 30 minutes due to the "late arrival of connecting passengers"......is a gross understatement!
Even though things seemed bad while in ORD.......everthing turned out better than I could have ever expected......as the pilot seemed to be flying that 767 as fast as possible (seatbelt indicator remained on for practically the entire flight due to a rather "bumpy ride"
) so that we arrived at LGA before the clock stuck midnight (actual wheels down time was 11:56PM). Talk about a close call.
Delta earned a hell of a lot of "brownie points" in my book (as well as my continued loyalty) on that day.
FWIW, I didn't quite have any status with Delta at that point....and was travelling on a Q class fare.
A.J.