They did the best they could considering Afghanistan is a difficult place to get replacement parts for anything let alone 20 year old aircraft. The ground engineers patched up aircraft to keep them flying for long hours I mean 200 flight hour a month for some guys. So it amazing how little the amount of accidents occuring considering the massive amount of obligations the military has put on some of the companies out there. Some operations we did that even american pilots refused to fly due to dangerous weather or enemy activity.
Because of the altititude in the north part of the country and the extreme weather conditions such as massive dust storms, severe fog and snow it makes it even more dangerous. In the north you have to sometimes fly nap of the earth because any higher and the aircraft would not function considing the 2000lb to 4000lb loads they are carring at times.
Those aircraft are amazingly tough and can handle abuse. We had one take a bullet right through its engine exaust and it kept flying. A second one took a round through the rotor blade and didnt even notice it until the after flight inspection.
As for safety. I have seen the companies fire ground engineers when they didnt know what they where doing so they did have a concern for it. I mean the Captain of each aircraft was in charge and if he didnt think you where providing him with the best service you could considering the conditions he would would refuse to fly the missions.
I have seen 2 exausts fall off in mid flight though. These russian aircraft are somewhat volkswagons of the sky. Easy to fix and get working in tough conditions but just as likely to break as a BlackHawk or an Apache. Hell I saw a Cobra heli come in damaged so no aircraft is imune to gremlins or un-preventable malfuntion.
Bottom line is the military would not be able to perform the logistical replenishment job by themselves as there is just to many places in need in that country (be it civilian or military).