I've posted it before, but I think that PHL would be spared significant downsizing if US and AA merge. JFK is capacity-controlled, so unless US-AA also buys B6, there won't be enough slots available during the prime afternoon/evening for all of PHL's European schedule. My guess is that JFK would continue to feature enough flights to feed the Europe, S America and Asia schedule and PHL would continue to see European flights as well. And maybe a flight or two to S America and/or Asia if there's significant O&D from PHL to those regions. If AA and US merge, the combined airline will be the largest in the world and could certainly serve both NYC (largest international O&D market) plus PHL (about the 5th largest metro area in the US). Perhaps not every flight would remain at both airports and perhaps some flights would switch gateways, but I think both would remain.