If you are a large fleet with many trucks, it would probably be cheaper to hire employees at the truck stops (or manage your own fuel depots) to just pump fuel all day for the automated trucks on the automated routes.

Then you could have a small number of vehicles, or small companies could pop up to serve this role, that refuel automated trucks that run out and stop driving outside those automated routes (if this is even a concern).

If you are eliminating 80%+ of trucker salaries, you have a lot of money to work with.