Wirelessly posted (BlackBerry: BlackBerry8530/5.0.0.1030 Profile/MIDP-2.1 Configuration/CLDC-1.1 VendorID/417)

I don't think any refund is due. If award space had opened up, and the OP had rebooked his Dad onto AA metal, then a refund of the BA-metal surcharges would be due, and would have been routinely credited back when the award ticket was re-issued. But that's not what happened here. Dad was re-accommodated by BA onto IB/AA flights; no refunds are due in that circumstance. If Dad had been originally ticketed on an AA/IB flights, and had to be re-accommodated on BA metal due to an AA flight cancellation, the BA-metal surcharges would not have to be paid in those circumstances. By similar logic, no refund of BA-metal surcharges is due in these circumstances.

If the resulting delay in arriving back in the U.S. was sufficient to trigger EU 261 compensation, then I would definitely pursue that angle.