I do not buy the sudden CB blocking the way , the 180 in a tight valley and the subsequent stall. Those guys were not amateurs ,they were locals to the area and knew the aircraft well. Anyone flying deep in the Alps knows how and when to go back ( and how to do, or not to do , a 180 in a valley, and with such a slow aircraft should not be a real issue anyway ),
The aircraft might not have radar but today with an IPad and Meteox you know exactly where the cells are and where they go . Finally a stall in a Ju52 would not pitch down the aircraft to a vertical dive as suggested .