Ok, are you talking about BASES or HUBS? It seems like alot of folks on here don't get the difference. Bases can be anywhere, but as far as hubs and focus cities:
DCA, LGA, BOS ops, the preferred Shuttle, all very valuable as seen time and time again. Keep in mind US shuttered BWI so Washington antitrust concerns may not be as big. The New York and Boston ops complement any other carriers presence in those cities (except Delta).
PIT- toast, regardless. Only a matter of time.
PHX- depends on the merger, probably reasonably safe. Might be in a fairly reduced state in certain pair-ups.
PHL- Safe as either major hub, or focus city/gateway dependent on merger. Again, could be significantly reduced in some link-ups.
CLT- Unless Delta, safe. Only other southeast hub, fills hole in most carriers networks.
LAS- Probably smaller focus city.
US and HP would remain most intact in a merger with NW. PIT and MEM would be sacrificed. With UA some of the US network would be trimmed, some would probably have more emphasis (CLT).
"Base closures"? We're talking about MAJOR capacity reductions, which I actually agree with Chug Parker that the industry needs. Entire hub operations and thier support will be dismantled, major furloughs in all areas, maintenance, training, res centers, headquarters, administration facilities closed. Express carriers discontinued in favor of larger aircraft, less flights. Huge fleets parked.
The next round of consolidation will be the real deal- the equivalent of, or at least the effect of one or two of the current majors shutting down. We're talking major industry reshaping, not hokey-poke America West hooking up with an already gutted, emaciated version of US Airways. The key word is consolidation.