Hello AutoGen_7139555

In The HMI there is a Systemalarm that comes up if the HMI connection is interrupted (140001/140000 I think) you can shot this in Alarm view.

Another easy thing is to use a toggle tag in teh PLC -> in HMI show this in the header or status bar as an animated circle or rectangle that canges color with this tag, so you can see if the signal is flashing everything is OK if it is not flashing then there is no Connection  (its not that smart but you can see it at the first glance )

Bye Murof