I was flying ATR 42/72 in the old (-300/200/212) and the new (-500) version from 1997 to 2004.
Crossing the Alps we had to do driftdown-calculation, especially for the ATR 72-200 in the summer for the planned route
The ATR 42-500 was safe at any MSA below 14000ft with MTOW and ISA +15.
Unfortunately I do not know the terrain on their route. Maybe somebody could post an enroute chart.