The User Business Continuity feature in Webex Calling provides the ability to automatically forward calls if a user's device or the entire group's devices become unregistered. This means that if a network issue or device malfunction causes devices to be unregistered from the Webex Calling service, calls can still be redirected to a predetermined alternate number, ensuring continuity of communication.
Cisco Reference
Cisco documentation on Webex Calling Business Continuity explains the scenarios and capabilities of call forwarding when devices are unregistered.