When an app is removed from the App store, it continues to function where it's installed. (Apple so far has not disabled nor remotely removed any app from anyone's devices). if you sync with iTunes, iTunes will capture the app and save a copy locally.
They removed this functionality. https://imazing.com/why-did-ap...
If you charge a fee for any book or other work you generate using this software (a âoeWorkâ), you may only sell or distribute such Work through Apple (e.g., through the iBookstore) and such distribution will be subject to a separate agreement with Apple.
Originally it was not worded to only be iBooks.
"An idealist is one who, on noticing that a rose smells better than a cabbage, concludes that it will also make better soup." - H.L. Mencken