It's all getting very technical and a bit off the mark for specific ATR ops.
Put simply the ATPCS system automatically arms during the takeoff roll, part of the takeoff procedure is to check it is active. If an engine fails the system up trims the live engine from 90% TQ to 100% (RTO PWR) and feathers the failed engine. Technically from that point the engine is secure! After acceleration altitude (min 400ft depends on second segment restrictions etc) memo items at carried out that confirm the ATPCS has functioned correctly and manually confirm the failure (PL, CL to FTR and FSO, bleed if live engine isn't within limits and performing). Form this point the engine is well and truely secure, the only way to unfeather the prop is to attempt a relight which I highly doubt occurred here, not enough Alt or SPD or time to go to QRH.
Now if they had already gone through accel alt and moved the PWR MGT to CLB the ATPCS function would have been disarmed requiring prompt action from the crew to identify and feather the engine. If not done quickly performance can be serverly degraded.
In a glide at VmHB the ATR does approx 2nm per 1000ft altitude, compared to other TP I've operated it glides quite well but from 1300ft you don't have much time to get on top of it.
For those interested Vmcl is 98 for F15 and F30 config.