I will agree there is a problem in the event of collapse of civilization. Certainly old hard disk motors will not survive too long. I don't know what the lifetimes are for the magnetic recordings but it's probably not great.

Alas, you probably will never find a market for a product just because it is likely to retain information beyond the buyer's lifetime. Except to the long now and archival folks. What are the lifetimes of compact flash and similar storage?