When any member alert subscription expires, that member will receive a short message on its desktop that its application copy has expired and it can contact the Alert Group Owner for renewing the subscription if required.
No alert message will be served to the member whose subscription has expired.
If Alert Group Owner renews the subscription after its expiry, member will have to activate the application again by entering its credentials (email and password).
But if Alert Group Owner renews the subscription before its expiry, member won't be required to take any action. Application will continue working as before in this case.
Please note that if Alert Group Owner has selected "Expires: No" while creating the member subscription, then the application won't expire till Owner itself expires / deletes it manually.