Amazon issue

If I am understanding you correctly that is concerning. I have an old keyboard kindle and once I finish with the book the option to delete is worded " remove from device" and as far as I am aware all of my books still exist in my account just not on the kindle, but I have so many who knows if any have disappeared.... I am tempted to started moving all my ebooks to calibre, at least I will always be ensured of having a copy on my hard drive. I always download my audiobooks and have them backed up on the PC and a separate drive after I encountered problems with itunes about 2 years ago and it became very painful to sort out. I am a firm believer that you should be able to do what you want with your electronic downloads if you have paid for them as long as you dont share them.

Certainly on older devices you should see both the options to just remove the download from your device as well as permanently delete. But on my Kindle Paperwhite with the latest software update I have the two options “Remove Download” and “Permamently Delete”.

You should be able to check whether your book is still in your account by looking under your account on your computer under the option to Manage Content and Devices.

On one occasion when I was trying to send content from the cloud to a device (Kindle), I inadvertently hit the adjacent delete option. Using chat with Amazon, I got them to restore it. I did a search for the title under my orders to find the date and order # of the purchase. The only thing is that the date associated with that title is now the date it was restored, rather than the date of actual purchase (when it was on sale).

If you can pull up the record of your purchase (they should also be able to do this, but I find it easier to have the information and let them verify it), and supply the information that you were instructed to do the delete from your device, and when that happened, they should be able to restore your purchased book into your account, and you should be able to verify that it’s there if you look under your account on a computer

I don't know if you're still tracking this thread but I've had the same problem for several years.
For me, I don't have the option to Remove Download (as in remove from device but KEEP in cloud) for older purchases. These books will have the single option of Remove Download but when I click on it it 'll ask if I'm sure I want to Delete. More recently purchased books have the dual option of Remove Download or Permanently Delete. I also don't always get the cover picture to display. It just has the title and author, words/no picture.

I've been an ebook reader going back more than 10 years and have a sizable library. A totally unscientific polling of about a dozen friends and family seems to show that this is just an issue with larger libraries. The cutoff for me seems to be about 2015. 2014 and earlier, it will only let me delete. 2015 is mixed. Purchases in 2016 and later have full options.
Covers will download on the Fires but I only read on an Oasis and a Paperwhite. I'm not sure what Remove/Delete options are available to me on the Fire--I never bothered to investigate since I just use them for the kids and occasional web surfing.

Deregistering the device is an option. Deregistering a Fire will remove all the content but on the Paperwhite and Oasis the content stays. You can remove anything you needed to get rid of while it is not connected to your account, then re-register. I've done that a couple times.
A factory reset will remove everything. Obviously, that's an option too. I usually have somewhere around 75 or so books loaded...2 or 3 that I'm currently reading, a few favorites, and my "planned" reading, which often goes off course. When I didn't want to redownload everything I did the Deregistering thing.