I think I know what's going on... I'm playing on sort of "custom hardcoe mode" with FWE, and the slave never reached Paradise Falls... well, maybe it would have helped if I didn't take his ammo and weapon (and clothes).
In this case the radio should transmit the line Grouse says when it happens: "you idiot, I can't make money from dead slaves", or something like that, and offer the possibility to buy another collar. Since, like MystykStar said, it is magic, let's use it to its full potencial...
Oh, what a hard life a slaver has nowadays...