I seriously doubt that truck drivers are going out of business any time soon. First of all, there's a massive fleet of trucks requiring drivers, and replacement trucks are expensive. Second of all, truck drivers also serve as a security guard. Even if we have self-driving trucks, I imagine they'll have a chaperone for a long time yet.
I expect that trucks driven by a human-computer team will be safer than trucks driven by either one alone.
There would certainly be some upfront cost to making tractor-trailers autonomous but they would save an expensive employee per truck, the trucks would arrive faster and more reliably, and they would save in fuel costs (optimal driving).
They would need to setup a way for the trucks to refuel, just an attendant at the truck-stop that would be paid a small amount for refueling them, or maybe a new kind of pump that would automatically fuel the trucks when they pulled up to them.
True, it's expensive to replace new trucks. But if it's a lot cheaper in the long term, it would be a serious incentive to push for the removal of drivers. And yeah, I too think that computers will get gradually implemented. Though I am sure the process will be 100% automated in the end.
The theft part is massive, if you had a truckload full of computer parts travelling down the motorway at 3am when it's dead. What's to stop some gang with tire traps. Bam! vehicle is over and they have 30 mins to loot before an error is realised.
This is possible in the current configuration, too. In fact, it may be easier to compel a human driver to keep quiet than a networked onboard computer relentlessly feeding speed, position, tire pressure and other telemetry to some sort of remote monitoring facility.
I expect that trucks driven by a human-computer team will be safer than trucks driven by either one alone.