I used a Barclays upgrade voucher to book a one way flight for two. I have changed my mind and now want to book a return for two using a 2-4-1. There is no avios availability on the outbound, and there is availability on the inbound.

If I were to cancel the booking using the barclays voucher, will the 2 avios seats booked on that be re-released? If so, can I quickly rebook before someone else takes them?

I think I remember reading somewhere that they are more likely to be re-released if they were part of the original quota of avios seats, if that makes sense. In which case, I did book these the moment they were released.

Thank you!