Human augmentation rather than replacement is key (at least in the early stages). Imagine a delivery truck with a set of drones on top. As the human drives (for now) and delivers, the human also racks up packages that the drones can deliver. In between deliveries the drones charge from the truck and when the truck heads back to base the drones who don't need maintenance tasks fly to the next incoming truck.

UPS in my neighborhood has done something similar in Christmases past--they have trucks bringing in bulk and bicycle delivery doing house by house. I didn't notice it this year; I don't know if it was a failed experiment or if I just missed seeing them.

War is Boring has an interesting post about using unmanned aircraft as a weapon-truck wing-man instead of an independent operator: https://medium.com/war-is-boring/64b87d155545