We know that C-mi will lose signal in the real world and have planned for it. You can control which mode C-mi will default into. C-mi will first pause and then go into "safe mode," where it will return to home and land.
C-mi avoids many objects by proximity detections. This helps with buildings and large structures; however, trees and cables are issues for all current drones on the market, and the user needs to fly in a responsible manner.