If you have enough drive space, you could back up all your media. I usually work on features, so once I have all the media, I make a backup to hard drives and keep it in another location.
But the usual presumption is that your original tapes could be recaptured if disaster strikes. Your work (how you put that media together) is represented in the project files. I actually keep one for every day (they are not that big) in case I have to go back to any particular version.