What happens to the swarm afterwards? Do they stay in the air forever? Self-land in a neat, organized fashion? Or do people have to go track them down? Also,

What happens to the swarm afterwards? Do they stay in the air forever? Self-land in a neat, organized fashion? Or do people have to go track them down? Also, what is the purpose of this class of drone? EDIT: Searching "perdix drone" surfaced more information. Perdix drones are the main subject of an experimental project conducted by the Strategic Capabilities Office of the United States Department of Defense which aims to develop autonomous micro-drones to be used for unmanned aerial surveillance.