At a basic minimum, A prompt needs to alert a customer when they are about to exceed the maximum number of discounts on a product (3 of the same game) warning them that going through with the purchase could void their GCU.
After that things A prompt to allow them to purchase the game without the discount and not affect their status.
At the VERY minimum a prompt would allow them to purchase it without being under their account which would not give grounds for BBY to terminate their GCU. This would still be bad for the customer as it wouldn't tie their account to the purchase meaning no points (let alone double points benefit of GCU for games). This could at least be circumvented by the customer by doing a report missing points through myRZ.com, but like I said not an option that's ideal for customers.