Create backups of KJots books on close (max 10 backup versions).
Remove backups of deleted books 7 days later.
That gives you a week to realise you shouldn't have deleted the book and recover it.

<a href="http://userbase.kde.org/Tutorials/Recover_Deleted_KJots_Books">http://userbase.kde.org/Tutorials/Recover_Deleted_KJots_Books</a>;