As a matter of interest, I've been witness to an Adventure Flight operator with a number of aircraft for quite a few years and to date I have NEVER seen the passenger choose to not sign the waiver before the flight, even when offered a full refund if they choose not to fly. The usual response is, "oh so I'm signing my life away," or "it seems necessary these days for these sorts of things."
I do seriously question if a tandem jumper would choose not to fly if the aircraft was not operated under an AOC. Hindsight is a great thing.