Re: "The satellite would thus know to keep one of its receiving assemblies aligned..."
Fail #2: the satcom equipment isn't in the 777's MEC (main equipment center), it's all in a equipment bay above the passenger cabin. I'd be interested to know if the AIMS units fall back to VHF if they fail to talk to the SDU, VHF won't be much use out over the sea. If you check SITA Aircom's VHF coverage maps, it's apparent where VHF coverage is avalable, MAS is a SITA Aircomm (rather than ARINC) customer. Inmarsat & Iridium provide satcom coverage to SITA (and ARINC).
Last year Boeing issued an Alert Service Bulletin concerning corrosion and cracking in the fuselage skin around the area of the satcom antenna (the aircraft has two, a high gain phased array for voice and data and a low gain 'shark fin' for low bandwidth data only). After months of discussion the service bulletin has been now issued by the FAA and EASA as a full Airworthiness Directive. That AD goes effective in April (next month).
I'd replace the fire scenario with a gradual depressurization scenario akin to the Helios Airways incident. My hypothesis is the mid Gulf of Thailand turn was instigated by the crew aware of something going awry, switching the a/p out of FMS control to action a simple heading demand but failing to complete it before being overcome. I don't buy the further right/left zigzag over the Straits of Malacca - it just went straight out over the Indian Ocean.
I read today that some old biddy on a remote Maldive atoll has told her local news website that she saw a big old 'jumbo jet' [sic] screaming over her roof later on Sat 8th March.