Well, the drive is definitely defunct. I spent the better part of the day trying to format it in Windows, which eventually gives up and can't access it. The Tvix also doesn't even bother, the drive is dead to it. I can still use the media streaming functions and TV tuner on the box, so the device itself is still good.
Unfortunately I don't have a readily available SATA drive hanging around to toss in the box and confirm 100% the original drive is toast. And while I appreciate the notion that hard drives these days are relatively inexpensive, my current budget right now does not really allow me to just pick up another drive on a whim (especially those in the size realm of the original or higher).
I'm also fairly upset that Digital Connection sold me the drive along with the Tvix and it's gone caput after just a year of use. I emailed them saying as much, and wondering if they would be willing to do anything about my predicament. I've never had any hard drive go bad on me in less than four or five years, much less one from Western Digital (which has always been my go-to choice for hard drives).