I'd expect them to have a lot of surveillance cameras on for this reason. Also as dashcams for collision liability, especially for the first truck vs. cyclist death incident.
To figure out which truck has the iPads and get away with them you'd need:
- an insider to know the time and content of the truck
- stop the truck
- unload the truck at the spot (it will refuse to move your way)
- deal with an alarm system (maybe lights and sirens)
- get away and sell all the high value goods despite their serial numbers
Should it become a problem we'll just ship all the boring stuff autonomously and the rest with a guard that needs no extra breaks and can sleep on the road.