"What we will likely see is a Delta-Northwest merger and although the Northwest CEO does not want to lose his job, he will not be able to oppose the board and stop this merger from happening. We will then have a massive Delta Air LInes with hubs in Atlanta (Memphis which is close by and tiny under Northwest will be closed), Detroit (Delta's smaller Cincinnatti hub will also close), Minneapolis/St.Paul, Tokyo, JFK, and a few other regional hubs like Las Angeles (LAX), Orlando, and La Guardia. This is my best guess based on my understanding of the two airlines.

For United-Continental, Contiental's CEO is against merging but admits they will be forced to merge if Delta acts. In this case, United will probably take over the smaller Continental desipte the fact the better airline operatonally (Contintenal) will be take over. All of United's Hubs (LAX, San Francisco, Denver, Dulles) do not cross with Continental's hubs (Guam, Houston, Newark, Cleveland) so probably no hubs will close in this merger. Ideally, Continental's management which is regarded as better will take over but that will depend on the negotiations and since United is bigger, is probably unlkely."