It's also hard to square with the fact that the satellite system was still pinging 7+ hours later. It doesn't appear to have been powered down at all, it just stopped sending ACARS reports. And so it wasn't powered down deliberately (or if it was, it was then powered up again), and it wasn't powered down by fire damage, even seven hours after "goodnight", and it wasn't sunk under water or torn apart by a plane crash within that time either. I think it's conceivable that that could happen as the result of the suggested fire accident, but it would take a very specific set of circumstances. And you'd also have to have an explanation for the other apparently contradictory information, such as the reported radar pings west of Malaysia and heading north, or (as you said) the later deviation from course. Doesn't seem likely.