It used to be you could find a box of photos or keepsakes that you inherited to look back on how things were or when you were a kid. Now, most of that is stored on phones, and most parents probably don’t think to share or save them in a way to be passed down in the future.
The best is to truly keep multiples. But flash storage would be more resilient and durable. Mechanical is susceptible to mechanical failure, impact, electrical shortages, etc. Both affected by heat, but if both were in a safe, my money is on flash storage if it were the only option.