Not entirely impossible. It depends on Banks and airlines.

Both Chase and SunTrust have clawed back miles. So as Fidelity Brokerage on their promotions.

There are some cases SunTrust clawed back DL miles months after deposited to the debit cardholders' accounts. The cardholders already redeemed the miles, but have not flown the itineraries yet. They found their DL accounts had negative balance AND worse, their reservations disappear.

Several years ago Chase did similar things on cards closed before the requisite 6 months period stipulated in the T&Cs. An Fter friend had the bonus clawed back 3 months after closing a card that did not stay open for 6 months. He PMed me and I went to check my account - same thing happened. We both received letters from Chase shortly after the miles were clawed back. At least Chase had the decency to inform you what they had done. SunTrust couldn't care less. People found that out when they discovered their award reservations disappeared.

Not saying this would happen to the Citi / AA scenario but it is no guarantee it would not happen, because if the banks want to, the claw back can definitely be done, although it usually take a couple months for that to happen, just when you think the coast is clear.

My guess is, if anyone plans on doing the quick cancellation, the best way to ensue you do not lose it on a claw back is to redeem and fly the awards asap like in the case of the UA 4 miles to Asia award tickets. Those who could fly in the next few days after this error, were able to finish their trips. UA honored their bookings so they would not be stranded somewhere in Asia. All others got canceled. DOT cited with UA in an indirect way on its ruling months later.