Buses typically make several runs along their route in both directions, until they need to go back to the barn for refueling, maintenance, or mileage. So any deadheading they need to arrive or return from that route tends to be a fractional part of the mileage they make on that route. Also, the route taken to and from the barn can be a lower-traffic route than that which the bus covers on its scheduled route. It's also a defined endpoint; if we see these robotaxis meandering around town with nowhere to go, except sometimes a random supercharger port, that is not deadheading, that's lollygagging.
A lot of buses will run empty going the non-demand way during rush hour. Like the D-line in Seattle where I live, if you try to catch a bus into downtown around 5 PM, one or two out of service empty buses will pass you by first since I guess metro thinks they are better off getting back to downtown more quickly than servicing off peak demand along the way.
