Drones are "manless" aircraft by terminology.  There are currently military drones that stay up for weeks a time and perform surveillance around the world, and also can run combat missions.  Several units fly of out the Dsm airport monthly and run missions abroad and come back with no pilot in the cockpit, all done from the office.

It's not if it will happen, it's when.  Everything can be sprayed by drone and/or robotic-ally, just give it time.