Reel to reel tape has a pretty good media lifetime if looked after well and you were lucky with your type of tape (and not everybody was!) but it won't last forever and the danger is that one day you won't be able to find a tape machine to play them on, and if you do the quality will degrade because it's analogue recording. Ralph Jordan had a huge collection of music on DAT and calculated that copying them all to another medium would wear out all the remaining working DAT machines in the world (they haven't been made for years now, and have limited playing hours lifetime) so we'd never hear all of it.

For ultimate long term storage, it has to be accepted that you'll be copying your data as media and machinery change. As it's digital it should be preserved accurately, but you can't bury it in a time capsule and expect it to work 1000 years later, or even 100 years.

As for routine music and other data on hard disks - backup up has never been easier. USB hard drives are fast, high capacity and ridiculously cheap and there's no excuse!

Offsite backups over the internet are easy too, though the storage is more expensive if you want a lot of it.