Hi Gary
Aaah, bummer !

I still have to do that one ( I HOPE NOT !! ) but I've done so many stupid things in calibre.
First of all:
MAKE A Backup, RIGHT NOW, SIR !!!
Now: I have a small test Calibre library and I tried the following:
1. Delete a book, within calibre library view naturally.
2. Calibre still open, choose windows wastebasket, restore folder
3. In Calibre choose Library Maintenance, and then Restore Database
Pauw, as far as I can see my deleted book returned in that Library, with the correct metadata ( saved in *.opf files for each book )
I DON'T KNOW if this CAN help you in any way !!
As far as I remember, the above depends on the books files, including the opf file, is there for all the books.
You might want to give it a try.
If you still have issues, I think you'll have to wait for the gurues to pitch in.
GOOD LUCK !!
Cheers, per