Offer the choice of reassigning notes/pages to another section/notebook when deleting a section/notebook

[nekohayo]

Deleting a "section" should not be a radical action. Deleting pages without warning/undo means catastrophic loss of data.
Quoting the GNOME HIG:

Anticipate errors

People make mistakes. Anticipating these mistakes will prevent damaging consequences, and will make your application more pleasurable and satisfying to use. The first line of defense here is to design your application so that mistakes cannot be made. Secondly, if it is possible to make a mistake, make it easy to recover.

Automatically correct potentially invalid input, and always make it possible to undo destructive operations.