I bought an award ticket for my sister to travel back in November. I remember the ticket costing 37.5K because the return trip ATL-IAH was in F. No problem, however over the weekend when I was in IAH my sister told me she didn't get an F seat because due to weather issues she missed her ATL-IAH leg and was put on an RJ later netting a Y seat.

Does Delta return mileage for this? I know I would've rather paid 25k for full Y trip.