[Adoby]

Typical recovery involves removing the hard drive and access it from another computer, without booting from it. Preferably using a different OS to reduce chance of virus infection. There are different types of docks for hard drives that can be used. And immediately copy everything on the hard drive that still is readable, if any. After that look at the copy and see what can be recovered. Perhaps everything, perhaps nothing.

Calibre backups metadata for each book as a OPF-file that is stored in the same folder as the book file. If you want to recover the metadata, then you need the folder intact with both OPF-file and ebook, and possibly cover as well.