Back then, one common practice for a driver who was stranded by their company like this was to drain the oil out of the engine, leave the truck idling at a truck stop or highway rest area somewhere, and then hitch a ride home with other truckers.
The company was then in a race against time to save the truck before the engine seized up. Even if they have GPS they may not be able to get there in time.
I wouldn't recommend this approach, of course. I think the truck is more valuable to the screwed driver if it's in working condition.
Prior to trailer or tractor tracking we could go months before finding an abandoned truck.