[Sirtel]

I hope you'll get your books back. It would be heartbreaking if not.

Always keep back-up copies - on external hard drives and/or in cloud storage (Dropbox, OneDrive and so on). Even better, keep multiple copies in different places.

Just a couple of months ago I inadvertently destroyed one of my photo folders by accidentally moving it to another location. Problem was, it was a huge folder and there was not enough space on my disk to do the move. Something went wrong and lots of photos just vanished, they weren't in the recycle bin either. Fortunately I had backup copies, so I could restore the folder.
Accidents and failures do happen.

My thoughts are with you. Best of luck.