I think they just shut down the 12v power which will cause the propane valve to close (unless it is stuck). So yes, If they sense the fire they will stop the propane, hopefully before the fire keeps spreading on its own.
An automatic fire extinguisher is great for the traditional fridge fire, where it leaks the ammonia and hydrogen gas out and is ignited by the gas flame. However, it won't do any good on a propane fire, where the fire is fueled by excessively high pressure propane. This is where having a fire sensor that actuates a spring loaded off gas valve (much like the ones used on older motor homes) would be great to have.
Having a stainless steel flame shield would stop the flame from spreading due to high pressure gas, at least long enough for a thermal switch to shut the gas off.
While that motor home looks like a mess, it is the plastic that did most of the burning, and remember the roof is made of styrofoam, that is why it is gone completely. I'll bet if Blll digs in the mess his flight jacket is still there, possibly in cleanable condition. Leather is very resistant to burning, that is why they were used for flight jackets. Much of the mess is the roof having fallen in on everything. Ever set fire to a small white styrofoam cup? it just melts and shrivels to a gooey mess. The Luan plywood burned as it is very thin and doesn't take much to get it going. The sidewalls are largely intact, except for the hole in the side just aft of the fridge. That is why I say the gas pressure possibly went high and turned it into a blowtorch. That one hole is not easily explained away.
I will be very interested to see what brand of gas regulator it had in it.
Charles