well, they don't sue individuals. They will make you sue them, draining all of your cash in court.
They will contact the gift card authorization center to tell them that the gift card sales were considered as abused. The gift card center will then cancel the value. If the gift cards are not used to purchase products yet, they will disappear from the balance or your account.
If the gift cards were already used to purchase products not shipped yet, the merchants will cancel your order. If the products were already ship, the merchants have to decide whether they should recall the shipment, because they might receive no money from the gift card centers. If the products were already received, they would ask you to pay for it as the gift cards were no longer valid.
Gift cards (not gift certificate) are considered as cash by laws. Exchanging $50 for $100 in multiples may be considered as money laundry, and tax fraud if you don't have license and do not pay for those extras you get.
Then we could also have a lot of people buying these gift cards from ebay or gift card exchange sites and there are going to be all kinds of confusions and disputes. What a mess this is going to be if BB go through with pulling the balance back.