I was thinking about a scenario and would like to get your opinions on it.
If you were running wide open and the throttle stuck open for whatever reason, your only option would be to shut it off. You would loose your power steering, but what damage if any would the engine sustain.

I have the CMI Sound Elimination mufflers on mine so I think they would clamp shut once the power is cut. That would keep the wave coming from the stern from entering the exhaust. But what about the water in the headers? Would it revert into the engine and cause a hydrolock situation?

What are your thoughts?

With the motor off and not turning you would get water into the cylinder(s) but removing the plugs before turning it over would clear the cylinders.
Once cleared, start the motor to dry everything out

I have exhaust tip flappers, doubt any water would enter.

I don't believe it would do anything at all. I have done that same thing many times. the boat comes to a normal stop and the engine would start normally with NO water in the cylinders.
That is called a plug test.
Full throttle - neutral - turn off key - check plugs.
You will still have steering just not power steering.

Doubt you'd have a reversion problem since the engine isn't even running by the time the boat sits back down in the water.

Now, It was on a bassboat but my father had the EXACT scenario happen to him 2 years ago on a big lake. He turned the boat back out of a finger, braced himself then pulled the kill switch lanyard.......then realized he screwed up and should have done that closer to the ramp he came from. Bass boats often have a foot throttle and the cable came loose inside the console loosing the ability to control it.