With PromoWorx, you can choose to receive email notifications when someone unsubscribes from your promo list.
How To Set Up Email Unsubscribe Notifications
Select Settings from the Top Menu and then select the Promotion Settings tab.
You can then tick the Email Unsubscribe Notification option and click Apply in the icon menu.
You will now receive an email every time someone unsubscribes from one of your labels promos.