Following mergers and name changes, most arena or stadium naming rights deals provide for a change in the name on the venue to the new name. Once US Airways surrenders its operating certificate and American Airlines is the name on all the flying, I expect the name "American Airlines" to replace the name "US Airways" on that building.
Other examples include the Bank One Ballpark (now Chase Field) in Phoenix and Pac Bell Park (changed to SBC Park and then changed again to AT&T Park) in San Francisco.
The name would change to something unrelated to AA only if the merger provided an out for either party (and one or both wanted out of the deal), and that's extremely unlikely. Near certainty that it will be named for AA.