Caudel claims that Amazon "secretly reserves the right" to end access to content that subscribers have purchased through Prime Video.
In response, Amazon said that subscribers who believe that they're purchasing a digital copy of content for all-time are actually paying for a limited license for "on-demand viewing over an indefinite period of time" and that this information is included in Amazon's terms of use.
At the end of the day, the content you pay for on Amazon Prime Video will likely remain yours, but in the world of digital media licenses, there's always a chance that a third party will revoke or modify Amazon's license, which then affects you.