I've seen transmissions lock up twice when a clutch went. The first was an 85 F-350 with a 7.3, clutch went at 12k (Ford screwed up the clutches for that year, WAY undersized), locked up the trans, truck had to be towed in for a replacement.
The second was a Chevy 3500, clutch went and locked up the trans. Truck had to be towed and my boss had to send someone with one of our dumps (it was a builders dump truck) to pick up the builders trailer and skid loader from the side of the road.
I've had slaves go out twice that locked up a trans as well, I know that a slave can do it, but I know that a clutch can too.