When taking the shadow server offline manually, will we receive an alert/alarm indicating that the environment is not longer in EP HA state?
No. As this is a manual request to shutdown the service, you will not receive an alarm. This is a "You asked for it" situation.
Now, if the service should terminate abnormally, then you would receive alarms/alerts stating that the environment is no longer in HA mode. An example of these messages is evidenced below:
[07/13/2018 14:42:52] CAUAJM_W_00168 The shadow's status is in question. The system is no longer in high availability mode.
[07/13/2018 14:42:53] CAUAJM_W_00134 The CA WAAE shadow scheduler has failed to update its status. Please investigate.
[07/13/2018 14:42:53] CAUAJM_I_40245 EVENT: ALARM ALARM: EP_HIGH_AVAIL
[07/13/2018 14:42:53] <CAUAJM_W_00134 The CA WAAE shadow scheduler has failed to update its status. Please investigate.>