There is absolutely no evidence the aircraft has been hijacked.
There is plenty of evidence to suggest that the aircraft might have been hijacked or commandeered, there is no proof.
Sure the plane might have had some kind of fire or other disaster but the timing is very telling. No better time to disappear than at the hand off. Could be just a coincidence but I kinda doubt it.
That all the com/tracking equipment failed seems deliberate. Sure some disaster could have knocked out all the communications and tracking equipment (or the pilot's ability to use them) but left the ping? Once again, I kinda doubt it.
Thus our missing 777 will be found somewhere between maldives and seychelles, imo.
This completely ignores the satellite ping evidence.
EDIT:
On the side of a possible disaster:
The aircraft might have been flying low to have breathable air rather than to avoid radar.