Amazon Prime Video is able to remove a video from your library after purchase.
We are contacting you regarding a past Prime Video purchase(s). The below content is no longer playable on Prime Video.
In an effort to compensate you for the inconvenience, we have applied a £5.99 Amazon Gift Card to your account. The Gift Card amount is equal to the amount you paid for the Prime Video purchase(s). To apologize for the inconvenience, we've also added an Amazon Gift Certificate of £5 to your account. Your Gift Card balance will be automatically applied to your next eligible order. You can view your balance and usage history in Your Account here:
As I said(probably) in another post, you own nothing since you sing up and accept the terms. They can change the terms when ever they want, they can remove videos when ever they want or the rights for a movie or series end. If you want to have something, find a provider that sells and lets download files, so you don't lose what you buy.