Ok, I'll jump in.. I don't normally speculate (I'm a heavy Captain for a US airline with a lot of overwater experience in an ac like the 777), but I will add this, with CPDLC, HF, VHF, ACARS and SATCOM, I'll find some way to get a message out under duress.. especially CPDLC, for it's a couple of key strokes.. would take me.. 5 seconds, tops.
- Chances of complete loss of comm on the 777, very, very slim...
- Bomb explosion we would have found the pieces long ago...
- I don't like structural failure theory cause it would have led to disintegration of airplane and then aircraft pieces would have already been found...
my theories fall into these two areas:
1. Hi-jack (terrorism from outside or crew)
2. Hypoxia event leading to incapacitation of all life on board.. (has happened in the past)