'onDeleteEntry' Event is not triggered when an Entry is deleted?
Bulk actions do not trigger their respective events. When you delete an entry (or multiple entries) via the checkboxes, you are performing a bulk action.

As a workaround, you can listen to the onBeforePerformAction or onPerformAction events, check to see if the action parameter to see if it's the action you're interested in and perform  your logic as necessary. *


  * Much of this answer was copied from my &amp; Brad's answers on this similar thread...