MEC fire
Yes this could be a cause of fire and lead to an accident.
However I am sure that the crew if being faced with smoke and fumes in the front end would go through the QReF and don mask and initiate a long shallow to a lower altitude as rightly stated by a dial in of the autopilot. (at the same time initiate other drills to do something to locate and react if at all possible to the smoke/fire) By this stage there would be four eyes and two pairs of hands on this going through check list. A busy time.
All crews of all types will have practiced this in the SIM many times.
Regarding the search in the other direction.
Lets face facts, one of the radar sites reported a radar hit at about the time it could be reasonable to assume this flight could reach if in fact it made a turn. Reported it was not transmitting mode S.
If the authoritys there did not fully investigate and search these areas then I am sure every one would be up in arms that they have not made all efforts.
This is a very sad situation for the industry regardless untill we know the full outcome and untill the DFDR and CVR are located and the data accessed wwe never will do. However its good that so many front seaters are responding on here with very usefull information.