What smacks me as odd is that the aircraft left it's cruise alt and descended in a straight line towards the Alps for 10 minutes without communicating. I'm not yet clear as to when the Mayday was made, if it was a mayday or if it was from the crew nut they had a lot of time to stick 7700 or give a radio call during the descent.
Comparing this to the 4000' loss of alt due to icing doesn't wash and If it was an emergency descent due to decompression why didn't they turn off the airway and away from high ground?