Accidentally deleted my Thunderbird Address Book

If you have any prior profiles, there may be an older copy you could salvage. the names are abook.sqlite and history.sqlite. click help>troubleshootinginformation, scroll to 'profiles' and click 'about:profiles' and then click the 'open folder' for any inactive profiles to see if the abook.sqlite file is there and shows that it has had some maintenance. If so, you could copy and paste into the active profile after closing thunderbird. OR, there is an addon, Mail extractor, that can search you message folder and extract email addresses from prior contacts and create a csv file that can be imported to the addressbook. this wouldn't solve all your concerns, but would rebuild somewhat. Otherwise, the file is gone.

The Address Book files are located in your Profile folder and have names like "abook.sqlite". The Address Book window has an Import button. If you have a backup of your address book files or, even better, your entire profile, you can import the backup into your working Thunderbird installation.

If you deleted the address book outside of Thunderbird, maybe they're in your system's trash folder? If not, and you don't have a backup, you're out of luck - that address book is gone for good.

If you have other similar address books, say, in Google, they can be imported into Thunderbird, so all may not be lost.