This is not plausible. Biggest flaw in this theory is that the pilot had many different options to make a distress signal to air traffic controllers and none were made. Instead of making distress signals, various transponders and signal alerts were turned off at different interevals over a period of time. And the plane was redirected and reprogrammed to change the flight pattern. If that could be done, surely a distress signal could have been made as well.....
It is absolutely plausible. How do you know that the pilot had many different options to send a distress signal?
First of all, it is not possible to tell when the radios were turned off. The only thing that would be noticed immediately is the transponder not squawking properly. The radios are powered by the left, center, and right AC bus. In an electrical fire, those are the first electrical buses taken off line. There is one transponder, a right and left flight control computer, and a center. The Flight management system is redundantly powered by the center AC bus and the Aux DC bus. The Acars is redundantly powered by the AC buses. Acars is not a system that anyone cares about if it works or not. Aircraft fly with them inoperative all the time.
So if there is an electrical fire or smoke in the cabin, the most likely cause would be something shorted out on an AC bus. If the bus is shorted that makes everything on it inoperative. It is exactly this reason that the Emergency procedures dictate that these buses be taken off line and reset one by one until the affected short is identified. In other words, in either one of these emergencies, the pilot would have immediately had to take action to land the plane. He could have accomplished this by simply changing the heading on the auto pilot, which is powered by the DC bus also so it would have worked just fine, or reprogram the FMS which is also powered by a DC bus. When you have a fire, emergency procedures dictate that you take actions to put it out long before you worry about contacting center. Now, if the AC buses were the cause of the fire, they would not get their radios back online at any time nor would the get their transponder back on line. Not being a dick but you are dead wrong. It is not only plausible but right now, the most likely. I spent 24 years working on this exact equipment and it makes the absolute most sense to me.
As far as the plane continuing to fly, that also makes sense as smoke inhalation would have incapacitated the pilots. The plane would continue to fly on its programmed flight path without incident.
Sorry man, but it is absolutely the most reasonable explanation and answers far more questions than any other theory.
Hope this helps,
FDC