Depends. A while back, I was looking for an old, relatively obscure but unimportant album, and could only find one copy on eBay. It was only a couple bucks, so I bought it, ripped it, and uploaded it. Now it's preserved and available.

I also had an experimental EP album I downloaded from YouTube that I really enjoyed. At some point the author took it down, so I uploaded it to archive.org, again for preservation and availability. Later the author found it and commented something like "hey this is my work, what's it doing here", so I took it down. But I still have it and I'll put it back up when they stop making music.

If it was something easily available for a few bucks, I wouldn't publish it. Creators deserve compensation for their labor too. They need to eat. For something that they're charging way too much for, and they're not hurting for cash, especially if it's not easily available, yeah I wouldn't have a second thought about pirating and republishing it.

In your case, with the 99% availability, I'd try to complete the torrent and seed in any way possible. If that's not possible, I'd purchase and republish, filling in the missing files if possible or creating a new torrent if not.