I keep a 50gb CF card in our Mark IVs at all times and swap out 16gb SD cards periodically and keep them separate from our gear in case of theft.
I once served as an expert witness in court while another photographer was being sued by the client. The photographer was a hack of the worst kind ripping off wedding clients.
I can tell you from that experience, being a pro photographer and charging market rates, the judge and plaintiff are going to wonder why you don’t have the industry standard of two slots in your camera if you have catastrophic failure.
The questions will be asked, how long have cameras offered two slots? How much are those cameras and are they typically used in your industry and by photographers in your price point?
They’ll most likely consider it an act of negligence on your part. What’s the likelihood any of this could happen to you? I don’t know, never? But all it takes us once and it will cost you way more than the cost of upgrading to a pro body with two slots.
And by the way, you probably won’t have the luxury of defining industry standard, pro, negligence, etc. It will be pretty tough for a defendant to explain why they felt a $2,300 body instead of a $3,000 body was adequate when charging over $3,000 per wedding or $150 and more per hour for an event. If the technology is there, affordable, and widely used in your industry, you can expect them to expect you to be using it.
But this is worst case scenario. Best case, you have a great contract and understanding clients and you’ve already refunded them a pro rate, half, or in full, for the loss. Which most likely would’ve gotten you better bodies with two slots as well....and kept your sanity and reputation in tact.