However, if the active SMS is not recoverable (RMA) and the cluster is broken, then all devices must be un-managed and re-managed.

Remember that when replacing the failed SMS, the new SMS will have a new serial (CERT) number. When the Primary SMS is replaced, the original information of the old SMS is still in the devices. Replacing the Primary SMS device with a new SMS does not update the management information.

To verify if there will be a problem when you break HA, you can run the IPS/TPS CLI command "show sms"

{}show sms
Allowed SMS IP address : 192.168.98.10
Device is under SMS control
SMS Serial Number: XXXX-XXXX-XXXX
      SMS Version: 5.5.0.204732
           SMS IP: 192.168.98.10
         SMS Port: 8162

If the output of the command shows the CERT (SMS Serial Number) from one SMS and the IP address of the other SMS in the cluster, then when you break HA, the devices will become unmanaged. If both the CERT and the IP address belong to the active SMS, you will not have an issue when you break HA. If the devices become unmanaged when HA is broken, the TPS devices must be unmanaged via the LSM or the CLI. Additionally, the devices will have to be removed from the active SMS and then re-managed.