His remark to dispatch was that he was returning to his vehicle, and I don't think he was expecting to meet the suspicious person there. Not saying that's wehre they met, just saying that the call paints a picture where Zimmerman was resigned to having lost visual contact, and was going to await police so he could point out where he last saw the suspicious person.
GPS on just Zimmerman wouldn't tell you "for sure" if he continued to follow the guy he lost sight of - and even GPS on both of them would not establish what each of them was seeing.
Incorrect. While the call does reflect that he had lost sight of Martin, the claim that he was returning to his vehicle was made in his statement AFTER the incident - not during the call.
The gap from the time Zimmerman opened his vehicle door to the time he acknowledged the dispatcher's "we don't need you to do that" is 18 seconds. When the call ends another minute and a half later, no only has Zimmerman not made it back to his truck, he changes his mind about meeting the police at the mailboxes. While not proof, it would seem to indicate that he was still looking for Martin. It is also possible that he DID give up at some point after that and was in fact returning to his truck -- but there is nothing in the recorded call that proves that.