There are several active customers (at least I believe they are still active) along the SLRG lines. The ones I know of are Irmey's Perlite south of Antonito, another plant just north of Irmey's Perlite, there are grain elevators along the line between Monte Vista and Alamosa which generate a few loads annually, there is the San Luis Central railroad which has a connection to the SLRG just east of Monte Vista, and there is the Coors plant in Monte Vista. The SLRG provides the only connection to other lines for the San Luis Central. Therefore abandonment of the SLRG would also cause the SLC to have no way to continue it's operation.
When I road the SLRG's passenger trains back in 2008, I was told that they were not making money on the passenger operations but they were being supplemented by freight operations by a railroad employee I asked about it.
The SLRG also has another revenue source. Car storage.
I really don't know how profitable the line is, but it is owned and operated by Iowa Pacific, which has been having financial issues as a whole.