I hate to say it, but really any professional photographer should take precautions for all kinds of equipment failures, light leaks and such. Digital media is no exception. There should never be just *1* media card, or even 1 camera. I have worked at weddings and other functions, and I have always, always made sure I had more than one of everything.

Having only one card, and then losing it is just plain unprofessional. How one gets to be a working professional, and doesn't learn this basic concept is beyond me, really. Nevertheless, he should accept his mistake and learn from it.

And hope neither husband and wife happens to be of the litigious lawyer persuasion...