I wonder if there were any Sigmets (or the European equivalent) out for icing in the area. The Malibu is certified into known icing but it's flight characteristics change a LOT when you've got ice on the airframe.
I'm afraid they won't find them. If they had an engine failure they would have had time for a "MayDay". Just going off radar indicates a loss of control (accelerated stall/spin) or the like. Ditching - WAY harder than you'd think. After the whole incident with Capt "Sully" on the Hudson, a couple of us tried it at Flight Safety in a turbojet sim when I was still maintaining my airline transport pilot certificate and let's just say were the "ZERO on the Hudson"