We have really put shelves worth of tape onto a single drive that cost as much as two 90 minute Beta SP's used to. Now of course you're saying what if that drive wipes out ? the simple answer is to clone it to another drive and moved it to another physical location as backup. This is a very simple and cheap way of doing things. If you are really worried, make 2 backup copies.
While a power surge or other electrical failure could take a drive out, with clean UPS filtered power this factor drops significantly.
If the next argument is, what if I can't access the drive 10 years from now because the interface doesn't exist ( EIA vs IDE vs PATA ), you should plan to make copies every 5 years. With 5 year transfers, you'll see your storage expand by a factor of 4 to 6 times in capacity for the same money as today. Another words today a bare 1TB drive is around $100 or so, 5 years from now the same $100 will buy a 6TB drive or storage unit.
The time and cost to bring your assets from the old storage to the new storage will be quite minimal once you have them in a digital format. Their value could be as they say, priceless.

