Hello DWGaffney,
Thanks for using the Apple Support Communities!
From your question, it sounds like you are concerned about space on an iOS device when it comes to your audiobooks. If these audiobooks are being purchased from iTunes, they are tied to your purchase history, so you have the ability to delete them and redownload them as needed.
You can redownload audiobooks in iBooks on an iPhone, iPad, iPod touch (iOS 8.4 or later), or in iTunes on a Mac or PC.
- Open the iBooks app.
- Tap Search from the bottom navigation bar, then search for the audiobook that you want to download.
- Tap Audiobooks.
- Scroll to find the audiobook that you want to download, then tap it.
- Tap the Download icon . The audiobook downloads to your device.
Download your past purchases - Apple Support
Cheers!