Patanom, I disagree with your views of rad alt.
If the aircraft hit a hill then the rad alt was 0ft. Thus for flight preceding that, at some time the altitude would have been between 0ft and 2500ft.
RA input to the basic GPWS would have warned according to terrain rise and aircraft descent rate; whether the aircraft could be recovered would depend on the time available according to terrain profile and crew reaction.
If EGPWS was working then earlier alerts would have been given so that a recovery manoeuvre should not be in doubt ... except for ...
Local research suggest that the 212 version of the aircraft would have been fitted with EGPWS vice a Thales alternative, although the latter is now standard.
Previous EGPWS accident in ATR 42
Crash: Trigana AT42 enroute on Aug 16th 2015, aircraft collided with terrain