Delta won't refund and you won't get any benefit for using your credit card. The credit from the ticket, less the penalty will be valid until the same Date in December of this year that you originally bought the ticket. All travel will need to be completed by that date. Odds are that the penalty to recycle the tickets will be at least $300.00, so not a lot of net value in the ticket.

I would definitely have the record split and cancel your friends ticket. Your reservation and price will not be affected.