I understand if the database goes belly-up you are potentially SOL (trust me, I get it. I'm using Media Pro and I'm in a bind because the program went belly-up). I do have 3 copies of all my data. My online drive, my offline/offsite drives & Blu-rays (hopefully shifting to cloud sometime soon).
But I only write changes to my online files. I do not attach my offline drives to update metadata on them (from what I've read of Peter Krogh's DAM book, it's a good practice to do it this way). If you rely on a database and your online drive fails all you have to do is buy a new drive, copy your offline drive to the new drive and make sure the database sees the new drive. Make sense?
I guess it's just pick your poison? Either rely on a database and risk it going foul or risk a drive failing and you loose the images and associated metadata (provided you aren't updating offline files as well).
Though maybe this is where a RAID would help (not sure which number RAID at the moment)? You can have a more reliable redundancy with a RAID.