Replacements don’t exist. Those old prop liners can operate off unimproved dirt strips, grass, even snow and ice - and off short runways too.

Jets don’t like that.

For back country missions the only thing maybe better than a DC-3 is a Basler... and that is a modernized DC-3 with reinforcements and turboprops for more power. They suck a lot more fuel than a plain DC3 though, which can be problematic as some of these fields they have to fly fuel in.