You can simply abandon the ticket and do nothing, or if it will have any value, you can call and cancel it. For most tickets, the remaining value will be on hold for a year from the original ticketing date, and when you want to use it, you'll then pay a $150 change fee. It's a domestic ticket, so the price of a roundtrip is usually half that of a one-way, so I am not sure why they would want to "refare" this ticket if you use only the outbound.

I don't know why you would have a problem with calling, as people's plans change all the time. Maybe someone else will be able to tell you if you will.