Transmissions
Some people seem to have made the error of stating (or assuming) that the pilots didn't make any transmissions after reporting INTOL (one post in particular seems to have been since removed?). The correct statement is that transmissions (apparently) weren't received.
If the first statement is true, the assumption might be rapid catastrophic airframe failure or that the pilots were far too busy until an airframe failure occurred.
If the second statement is true, a far larger number of possibilities open up. In an area with no radar coverage and unreliable radio contact compounded by huge electrical activity, the aircrew may well have been transmitting and not being picked up. Perhaps even in a controlled descent.
An extremely unfortunate note is that (if the Norwegian news story is true) PAX have superior communications technology available to them via satellite uplink and the most reliable company communication is a similarly uplinked automated fault annunciator useful to company mechanics and operations managers but woefully inadequate to address infinitely more pressing matters.