I've gotten that refund in the past (downgrade due to ATL ground stop IRROPS recovery) but I had to proactively call it in and then it had to get escalated to a second level CS rep who could pull the record for the original booking including cabin/fare class and not just the record for what I actually flew. My kettle self didn't get a voucher but did get 10K Sky Miles for service recovery in a related screw up on that ticket during the same IRROPS event.