Hi 
Is the bibliographic database a separate file and can you still see that file
where you saved it? Is likely to have been saved by LibreOffice in one of it's
own folders such as
/home/user/.libreoffice/3/user
Hopefully someone else will answer fairly soon with a better idea of where these
things are. I have cc'd this email to the Documentation Team as there might be
someone there more familiar with the issue. It's not usually a good place to
ask but this case seems a little unusual to me.
Good luck and regards from
Tom