Well, thanks for all the posts guys!
I don't know why I didn't think it was a driveshaft in the first place.
It's a matter of psychology I suppose, move a lever, nothing happens, must be a fault at the end of the lever. Short-sighted, but that's human nature!
As soon as the guy told me the light came on

so to speak, it all fell into place in my head.
As for driving home, given that it was the shaft that was broken, there was nothing to get wound up by having the CDL on. If it had not been a broken shaft then there was potential, which is why I made efforts to keep one side of the truck in the "marbles" or on the grass.
Sadly, I wasn't clever enough to know how to disconnect the auto CDL in Low, because if I had done that I would have known straight away that it was a broken shaft. (it wouldn't have driven at all with the CD open).
Anyway, it's all good news, as it turns out.
My concern about the CVs is not shaft related at all, just that they're 7 years and 180k kms old, and the guy has the whole front axle stripped down at the moment. On full lock, the passenger side was starting to click, so I think I'll change them as a matter of course.
The shafts themselves were renewed 7 years ago too, and I'm surprised one broke, but I guess it's not an age related failure.
We put these trucks to the extreme of their ability sometimes, because they're so good at it! It comes as a surprise when they eventually fail.
All's well that ends well, I say.... not quite ended yet, but it soon will be...

. Thanks for all your encouragement!
