Firstly, it will not affect your buyer feedback, worry not, a seller cannot leave neutral / negative feedback for buyers if they do, eBay can be asked to remove it, but a seller would not leave bad feedback for this .
You have 7 days to pick up an item after being notified it was in store, after that the store can either send it back to the seller, give it to charity or even destroy it. In my humble opinion for a busy store such as Argos, the easiest option would just be to bin it !
However, drop the seller a message explain the circumstances ask if it has by chance been returned to them. See what they say.
@carl7105