This rail line still exists intact, today, It was incorporated into the ever-growing Greater Seoul urban rail network (still often loosely called a 'subway') in 2009. I remember when that happened, as I was living in Ilsan at the time, through which it passes. One station was only 10 minutes' walk from my workplace.
I have ridden on this rail-line more than a few times. It is pleasant to ride, and takes not more than a half hour between Ilsan and central Seoul. You can ride it today way up north, to within a stone's throw of the DMZ.
I have even walked through Dorasan, the northern-terminus station of the line.