If the fare purchased is non-refundable/chg fee type (most are) then you'll simply get an ecredit good from one year from date of first planned travel on the ticket. It'll either be for the fare amount - change fee or if they waive it for the fare amount. Nothing is lost as long as you book another ticket using the funds before they expire. You don't lose any money since the value of the ticket is place on the ecredit. Just because the form of payment was a GC doesn't mean you lose that value and only get what's remaining.

If you end up being able to make a claim with Chase it'll at most be for the amount charged. Note that just because you don't use the ecredit doesn't mean that Chase will issue a refund. Chase only pays out if DL refuses to waive the change fee. If DL waives the fee, then you've been made whole. If you then don't use it within a year is irrelevant to Chase. In that case they see it as you had been made whole. Just because you throw the money away (by letting expire) isn't their problem.