Regarding the missing communication:
This may be an indication that something went wrong much earlier than initially thought.
But it doesn't have to.
When looking at NTSB accident reports (mostly GA planes admittedly) you will notice that in a very high number of cases if not even the majority of fatal accidents no distress calls were made by the pilots.
Especially in those cases where the pilots are fighting the plane hoping to be able to save it very often the comms remain silent.
Only when they realise there is nothing more to do e.g. shedding a wing or the rotor (in case of a helicopter) the percentage of distress calls appears to rise again.
So if a critical situation developped very rapidly out of the blue, it wouldn't be so much out of the ordinary if no radio transmissions were made, especially so far out over the ocean.