("There's no tangible motive and no evidence whatsoever of foul play.")
Neither is there any evidence of medical or self harm. Do you not think medical/self harm would have resulted in him/his body being located by now, either in the nearby fields or some hospital ward? Equally, a planned fraud seems illogical, Did not take his money, and leaves the truck, loaded, and hindering traffic. Msg there is I am gone, SHAZAM....
All kind of questions right off, why, how, and with whom?
Could have bailed immediately after changing clothes at home and departing for the load. Seems like a waste of energy and time he could be making tracks to go load, get nasty, haul, park then join to leave.
As an aside; considering all the praise for his work ethic, the caring for animals on his loads and being so dependable,
seem to be at variance to him planning to skip out, but under load...