subscribe expired notification

[Vinh Nguyen \(vinguye2\)]

I looked thru the WS-Notification specs, and it doesn't say anything
about sending a notification to a subscriber when the subscription
expires or is destroyed.  Does anyone know if this is a requirement?
When a resource instance is destroyed, Muse doesn't send a notification
about it.  Also, when the subscriptions are destroyed along with the
resource, no notifications are sent either.
 
I assume these types of notifications are something we must implement,
if it is not a WS-N or WS-RL requirement?