READ THE MANUAL, ok it is returned to the spot where it last touched the ground/robot last
Quoted directly from the manual:
<G9> It is expected that Scoring Objects may unintentionally leave the field during match play. Scoring Objects that leave the playing field will be returned to Zone from which they exited from (e.g. The Zone where the Robot was that launched it or last contacted it on its way out of the field).
It is returned to the last area it was in. If it is being supported by a robot it is considered to be in the same zone as the robot. If the robot is in two zones then it goes in the high scoring zone. Sometimes it will bounce out of the field. In this case, it is returned to where it touched the field last.