Some data points.
July 18th purchased a 340 dollar refundable ticket used 2 €50 dollar Gift Cards and paid the rest with my platinum Amex card. The 240 showed up as additional collection and on the 20th of July I got 200 dollars airline reimbursement.
Now I'm going to wait a couple of months and cancel the ticket and hopefully Amex can’t claw back the airline credit.
I’m assuming Delta will just issue another 100 dollar gift card to me. The rest will go back on my platinum card.