I've observed the same behaviour with one of our Apps - if the App is offloaded, the device will continue to recieve push notifications. Since the App is (effectively) uninstalled, it seems that there's not delegate to call-back to, and touching the notification banner does nothing, doesn't even show a message that the app has been offloaded that you would see when you touch the App icon.
This behaviour persisted for me for a couple of days, although I haven't tested longer than that to know if it the APNs token remains valid indefinitely. I likewise was unable to find any definitive developer documentation about how offloaded apps effect push notifications (or technical documentation on offloaded apps in general). Were you able to find any information Sumanth?