We booked economy seats with Delta using our credits, then were offered a cash upgrade to Business for the long-haul portion of our trip (Atlanta to Buenos Aires) for a decent price - considerably less than if we had booked our whole trip in Business. When we had to change over to Santiago, we were able to get the credits we had used back to apply to Santiago, but the fine print says that cash upgrades are not eligible for refunds or changes.
However, I’m not faulting Delta. This will be the 4th time we’ve tried to fly with them. They’ve been the best airline out of 4 we’ve dealt with for Covid cancellation issues over the last couple of years. I did look into just taking a flight from Buenos Aires to Santiago, but just felt 2 connection, both outbound and inbound, with lengthy layovers, and increased probability of lost luggage was worse than biting the bullet and taking the loss.
And we are really, really looking forward to this trip!