I don\'t currently use any apps that have an in app subscription, so I am not sure what the UI looks like in iTunes when do an in app renewable subscription.
I assumed
Recently Apple introduced their new service called "Status Update Notifications" which in essence is simple webhook that's being called when certain events occur on Apple servers. One of these events can be "CANCEL" when Apple's customer support cancels user's subscription. You setup a webhook and they send you a notification with details about this event. More information can be found here: https://help.apple.com/itunes-connect/developer/#/dev0067a330b
I added this reply because this is what Apple recently introduced.