In the days of analog tape recording, the one thing you could say about tape was that it was permanent. Once you made a recording, you could rely on it being safe for years as long as you didn't erase the tape, physically damage it or lose it. Granted, there was a period when tapes were made that didn't perform too well after years of storage. But even then, those tapes can be recovered and the recordings copied.
Digital data however is a whole new game. Digital recordings have a habit of being here today, gone tomorrow.
We can separate out digital recordings into tape recordings, audio CDs, and computer data discs. Digital video tape can be surprisingly reliable, but not digital audio tape. Digital video tape is used as an archiving medium by broadcasters and production companies all around the world. Metal particle tape has outstanding reliability when stored correctly. However, digital audio tape formats have worked very close to the edge of what is possible. DAT is a format that didn't really work at the affordable level. A tape recorded in one machine would often glitch when played in another. However, professional DAT machines are very much better at following the contours of a less than exactly straight and flat tape, and if you thought an archive DAT was unplayable, it might just be recoverable on a professional machine.
Audio CDs can be good archivally. I have factory-pressed CDs that are over twenty years old and play perfectly. Just a few CDs in my collection however have acquired a brownish tinge, although they still do play. Recordable CDs made with the superior phthalocyanine dye are thought to have an archival life span of more than 100 years, which is plenty good enough for me. Another advantage of an audio CD is that if part of the data is damaged, the rest is playable. The player simply plays what is there.
All computer disks, magnetic and optical, have the troubling characteristic that one day they can be working fine; the next day you can't get any data off them at all. The reason for this is that data is distributed over the disk, and a record kept of where the data is to be found and in what order. Lose or damage that record and the data is pretty much unrecoverable, except sometimes by horrendously expensive data recovery services.
The answer to all of these problems is to back up your data. Then if data is lost, you have a copy. But remember that the copy ideally needs to be on a different medium that is subject to different characteristics of degradation. Also, keep your backup in a different building so that it is safe both from fire and theft.
Check the integrity of your data and backups regularly, and also check that backups are still restorable – a process that doesn't always work as well as you might think it would.
Alternatively, you could take a different approach and work completely without backups. But that's a different story for another day…