Never played the demo, but this sort of thing is a reminder for me to make liberal use of my Sharkport (lets you back up memcard saves on PC, or download saves and port' em to the memory card).
Not to sound overblown or dramatic, but I feel like the loss of Memory Card data is one of the worst things that can happen to a person. Someone can rob your TV or sideswipe your car, but a memory card save is something you can never get back! I really am being serious. I feel bad for these people!