The only method that I have used to show operations when a processor has stopped (fault or program mode) is another PLC exchanging data, and detecting a heartbeat lost.
PLC A puts data for it's HMI into a data file, N43, which is read by the HMI and PLC B. One of the registers in N43 is a heartbeat, which increments regularly, like every second.
If PLC B reads the heartbeat register in PLC A and sees no change in the number for 3 seconds, PLC B writes 0's into the whole N43 data file in PLC A. 0 in the status word for each of the devices happens to mean power lost, communication lost, not running, in maintenance.
It's not elegant, but it works.
It gets complicated when you have more than 3 PLCs. PLC B monitors PLC A, PLC C monitors PLC B, PLC A Monitors PLC C.
THIS NEEDS TO BE VERY WELL DOCUMENTED! It is quite confusing to have another PLC change data within the PLC you just switched into PROGRAM MODE. This is the only time I WRITE to another PLC instead of READING.