Is the supply voltage for the controller and LCD, and opto and gate, really connected to the mosfet drain ? Maybe they can be separate supplies, and then the opto might isolate the controller IC, if the mosfet blows up from gate to drain.
I'm not looking at that right, but if there is 2 high side supply rails, them maybe the opto could still help isolate the IC (IDK how easy it is to short them side to side when they fail)