Tires blowing out are a much bigger (in terms of simple cost and the thornier problem of schedule optimization and ability to guarantee precise delivery times) and much more common of a problem than mechanical breakdowns. They're also a problem that does not go away with autonomous trucks or electric motors or anything conceivably around the corner, outside of some miraculous development in materials science.

As such, a (somewhat) well-organized industry has developed around getting replacement supplies like tires and other accessories to the site of a breakdown as quickly as possible, and this would simply need to be extended to include whatever it is autonomous trucks would require that doesn't touch the road.