All technology and infrastructure needs maintenance. Sure there will be drones. However, there will also be companies and people that specialize in creating and maintaining the said drones. Additionally, the shock and immediate disruption that we all are expecting out of this is flawed assumption I think.

I do however hate to admit that it might be possible that the world simply wouldn't require as many humans to function (birth rates are already declining in developed countries), however, I am too sober to have that discussion right now :D.