I have to think this is killing gnats with a sledgehammer. Am I missing something? Why not just remove the 120V power from the layout with a trip, why all the high current relays? One big control relay on the input power and then any sensing you desire for the power districts.
I too may be missing something but isn't that a Catch-22 situation? That is, if you remove 120V AC to all 4 bricks then obviously all 4 brick outputs immediately drop to 0V (including the brick that is already at 0V from its derailment trip). Now there is no indication of which brick tripped in the first place. I think it's kind of neat how there are 4 "micro pilot lights" that run to the top of the board that directly indicate the status of each brick/block.
OTOH, I suppose one could say it's obvious by looking at the layout to see which block caused the problem, feel each brick's reset button to see if popped out, etc..
Then, after MOW clears the derailment and resets any brick breakers, how do you "restart" the safety circuit? That is, all brick outputs are now 0V so the sensing devices are continuously trying to remove 120V AC. I suppose it could be as simple as a momentary bypass switch...but, as they say, the devil's in the details.