I no experience lah but watching tv had seen US coast guards helicopter finding fishermen in Baring Sea after their crab or fishing boat sunk in heavy weather with only reference point given by boat captain before boat sank. The MAS have the last position of the plane before its transponder fail, surely the MAS equipment is better that those fishing boat.
I am not familiar with where the aircraft went down, but in some parts of airspace there are no radar coverage because of distance. And oftentimes, the pilot needs to check in by some specific beacon