Audible book disappeared

Here's a reason to keep backups. I was just poking around at Audible, checking on some authors, and happened to notice that a book I was sure I'd bought and listened to was missing--presumably having gone out of print in audio version. Curious, I found said book in Audible Manager, but it's not listed at all in my Audible library, and I don't see any way to re-download it.

As I routinely delete Audible's aa and aax files from my hard drive once I read a book, if I had relied on Audible's cloud, I'd apparently be out of luck. Happily, I convert and save the mp3 files.

This is why I don't trust the cloud.