Just got an e-mail from AA talking about the merger. There is a strong hint in there (by omission) that the Barclay card will not be in the picture after the merger:
Same great benefits with the CitiŽ / AAdvantageŽ card
Your credit card benefits will remain unchanged. You'll continue to earn AAdvantage miles for purchases on your CitiŽ / AAdvantageŽ card without disruption.
No mention of the US card.