If you deleted the configuraion files, and you didn't keep them backed up, then they are gone.
You will have to re-run calibre -- it should open the Welcome Screen asking you to select your library.
Or use the Quick Switch toolbar dropdown to open your library if you already went past that.
You will have to re-configure the settings of course...
P.S. I hope you didn't mean you deleted the actual library folder, that would kind of stink!
If so, see the data recovery specialists.
