The early 24 valve trucks are extremely vulnerable to lift pump failure. It is by far the greatest weakness on these trucks and has frustrated me beyond words a few times. I know this doesn't help your dad, but what I did to avoid this problem (I have been stranded as well, never again), is to have a spare pump tied into the plumbing. I run an AD on the frame and have the OEM carter pump mounted on the side of the block. In the event of a failure, it's a matter of switching 2 ball valves around, unplugging the AD from the vehicle harness and plugging the Carter back in, and repriming the system. He could also carry his OEM pump with him on longer trips, but then your stuck changing a pump on the side of the road and may be forced to do it in the dark or less then favorable weather...
I hope he is able to get back on the road in short order.