I would pursue the search with Delta as there are more honest people than you think. They recover an incredible amount of items each year, most go unclaimed. Would definitely followup with calls to get to talk to a real person.
More disappointed the GA didn't try to find it as the plane was still parked there. Not great customer service.
Also, for others reading this, make sure you have your name and cell number somewhere on/in computers, headphone cases. Makes it real easy to reunite lost items.