Yeah, the magnetic disks themselves are going to be pretty reliable. But you may have to pay for an expensive data recovery service to get to the data on them. I've probably had a dozen hard drives fail on me personally since I started using hard drives (around 1993). Only once or twice have I been able to coax them into giving up the data. I guess the typical failure modes of a mechanical hard drive are that either something electronic fails, or something physical fails (stepper motor or whatever). In either case at least most of the data is probably still locked away safely on the magnetic disks themselves and can be recovered with the right equipment.

I don't know about SSDs. It seems unlikely all the memory chips would fail at once so I would assume that with the right equipment data could still be extracted from working ones somehow. But I guess there's a lot less you can attempt without specialized equipment. I would think though that eventually SSDs would be a lot more reliable than mechanical hard drives. There should be less to go wrong with solid state. I've never had a CPU or memory fail in a computer under normal circumstances. Just hard drives and power supplies. A couple of motherboards but I'm pretty sure those were the power supplies' fault too.