Have you checked at the KoboBooks.com website under the "My Library" section.
Check all three listed locations;
I'm Reading -->
http://www.kobobooks.com/library/reading.html
Purchased -->
http://www.kobobooks.com/library/purchased.html
Trash -->
http://www.kobobooks.com/library/trash.html
If in Trash you can select the books and do an UnDelete.