In the past we experienced accidental course deletion several times. Unexperienced users delete a course because they don't want to see the course in their author list anymore, e.g. when they are co-authors and don't know why.
The delete dialog is not very scary. Pressing the ok button is simple, a bit too simple for an action which has so many consequences.
The goal of this issue is to make the delete dialog more obvious and more aware. A solution could be to add checkboxes the user must check to really initiate the deletion. Another solution could be to make it a wizard like the close workflow and explicitly list the number of users removed, etc. and offer things like download of a backup file etc.