There have been other murder/suicides of this kind (assuming that the theory is correct). Particularly SilkAir 185 and Germanwings 9525 (I think there is at least another one, but at the moment it is escaping me). In fact, my impression has been, for a long time, that MH370 is itself a copycat of SilkAir 185 where the suicide corrected the mistakes that led to the discovery that the accident was in fact caused by the captain.

I'm not particularly concerned about this, after the germanwings incident in europe and US (and possibly everywhere else as well) flight decks are required to always have at least two people: if one of the pilots wants or needs to leave one of the flight attendants must take his place.