Purely anecdotal, but I've never had a hard disk just outright fail 100%, they always start going click click click on certain areas of the disk, and avoiding those files you can rescue the rest. SSDs on the other hand, I've never had one properly go into a "read-only" soft fail mode, they just fail to show up one day.

This is all among consumer drives though, enterprise stuff probably behaves better?

I'd love to see some kind of statistics on actual failure modes, but aside from Backblaze, everyone keeps their storage statistics private.