If you aren't familiar, the Amazon Underground offers a bunch of apps for free (including IAPs). The downsides are user tracking, pop-over ads, and the possibility of the app not working if there is no internet connection.
Once a person "buys" an app in the Amazon Underground, it is listed in the associated Amazon account. (I put "buys" in parenthesis because there is no charge.)
If the app is later removed from the Amazon Underground, does the "buyer" get to keep it?