I converted my Citi AA Platinum to a Mileup card a couple years ago but I did not bother to check if the account numbers remained the same. The main benefit you get from converting is that your credit history from the account carries over, as length of account history is a part of the credi score equation.

I also have the Barclay Aviator red which really overlaps the benefits of the Citi AA Plat card, and like the original OP I chose to keep Barclay open due to larger credit line.

This year when AA had a 60k signup bonus for the Citi AA Platinum I got another signup bonus as it had been over the 48 months window that made me eliable for a new offer, I still have the mileup card open.