The masters still exist, I'm told, but that's no good to anyone - they won't be re-released because it would require too much intellectual property wrangling and nobody cares enough to bother, and sooner or later that hard drive will die and that will be that.
Edit: Wait. Am I part of the problem?
If you want more, look either of them up.
Meanwhile, a lot of unique live-concert recordings (often made with the band's permission, unlike the Salinger tapes) vanished with the demise of What.CD. Presumably some people still have them, if bit rot hasn't caught up, but they simply ceased to be available.
I'm not sure these ever landed on torrent sites, but the first album from Godspeed You! Black Emperor is considered lost, and Eminem's debut EP was unavailable for more than a decade. Both are (early-)digital-era works, which raises interesting questions about the fragility of even modern content. The archive-less disappearance of quite a few online short stories, flash games, and Soundcloud tracks makes me suspect that in a few decades, quite a few more "first works" of notable creators will be unavailable.
Years ago, I was on a university private tracker. It was used more to share hard-to-find resources than for any actual piracy, much less piracy of anything new or policed. (I'm sure people stole plenty of 50-year-old textbook PDFs.) But when the hoster shut it down abruptly, everything simply vanished, including all kinds of hand-scanned and annotated stuff which may be literally irreplaceable.
Meanwhile, something like Kickass Torrents can be shut down and abandoned by the owners, but the content all reappears almost immediately. The private-tracker model has lots of advantages for community building, but as far as robustness it undermines the entire concept of P2P sharing.
It's sort of funny to see that even something released post-internet can float in and out of availability like that. I generally class recent content as "lost" or "available", but obviously there's still a third category.