I'm not certain you wouldn't be able to fly. I have had the experience of the boarding pass scanner objecting to my boarding pass and being told that my itinerary has been deleted because they show me as missing my initial segment. When I protested that I had in fact been on the first segment, as evidenced by the fact that I was now standing in front of them, it only two a few minutes of rapid-fire keyboard action to restore me into their good graces. They assured me that my return ticket would be fine and it was. I didn't receive miles for the first segment until I did the "missing miles" thing on the website. So it is at least possible that you could talk your way out of it. Perhaps they were able to somehow confirm that I really did take the first flight, I don't know.