Not sure where you read that. Obviously, the DB (guide data and settings, etc) stored on the device will be gone if you reset or replace it, as for your external drive…
If you replace your DVR, they have a process to move your drive/recordings to the new device -
If your tablo dies… and not your drive, well you can still access your files. Maybe use that method if you get a new tablo. Or try to “export them”… just that the information as to what show is what is lost on the tablo - so it could be a nightmare sorting through them if you have 100’s or even 1000’s
don’t believe everything you read on Fbook!!