FWIW, you keep all audible purchases even if you cancel your subscription (regardless if they were bought with credits or cash). So you can cancel and continue using the Audible app as you have been. You need to use all your credits before you cancel though, IIRC.

That said, it's very easy to remove Audible DRM. Each of your purchases is encrypted with the same short series of bytes. You can fetch them by uploading any purchase to this site [0] (also open source). Then, FFmpeg supports the `-activation_bytes` arg for this exact purpose:

    ffmpeg -activation_bytes <ActivationBytes> -i <Input>.aax -c copy <Output>.m4b

Alternatively, Libation [1] is a great open source app that simplifies this process. It's a little rough around the edges, but it gets the job done!

[0]: https://audible-tools.kamsker.at/

[1]: https://github.com/rmcrackan/Libation