I'll have a crack at it.
Is this going to stay shut down? Manual reset?
What I am thinking about is 80V, then loaded with a large load will drop more than the 2V, and it will oscillate. Relay will chatter to death.
If it will latch, finding a load that matches will be a problem. It probably will not shut down completely, more slow down. Cube square vs linear voltage vs fixed resistance?
Slow DOWN is still much better than blown UP.
If it is going to latch, maybe add a 555 and a second high power / low resistance load 5 seconds after the 1st load comes on? It would get it closer to 'shorted' without doing it all at once.
Parallel fets can be a problem. They need derated for some extra safety. And use gate ballast resistors.
If possible, best to have a separate load for each fet to get around a few of the issues. The fet tabs should be isolated from each other (depends on the type of fet).
Not sure about this... contact bounce. If the relay is fast switching, then the fet will be running faster, more cycles than expected, more time ramping the gave voltage down, more fet heat, etc.
Probably not much of an issue.
Not sure about this either... SSRs and lightning. The SSR will be out there on the power wires. I could imagine a regular old relay may have a better survivability % than an SSR.
This is what happens when I wake up too early,
G-