If I understand your scenario correctly, you want to know whether a View is added/removed to a region. If you do not need them to be removed,
but just deactivate it, Prism provides a way to do this. The IActiveAware interface allows you to monitor Activated/Deactivated events of a View related to a region. The following thread provides more details about this:
Another possible approach, could be finding a way to persist the View’s state, so when you load it again you have access to the objects
that were cleaned up.
You might also implement the
IDisposable interface, and the controller whose responsibility is to manage the lifetime of that specific view, should call Dispose() on the view, so the view can now clean up the resources.
If I misunderstood your scenario and when you said
“knowing when an element/view is really destroyed” you meant about to be GCd, you can always use its destructor.
Please let me know if this helps.