I agree with Bob.
I do not seem the harm in hypothesizing what effects the demise of one carrier will be on the others. Airlines must do it lest they be deficient in their fiduciary duties to their stockholders and BOD.
I can remember well about a year ago when folks were talking about the pieces of US: NW gets PHL and the A330s; AA gets the Shuttle and DCA and LGA; CO gets CLT; the crows get PIT.
These discussions are logical and strategizing on the part of the airline. While everybody certainly does not desire that folks be laid off or lose their sources of benefits, everybody must assume that plans are in the works to fill the vacuum that would certainly be created.
Bronner has already discussed it, Texas Pacific has already discussed it, Icann has probably discussed it, and I am sure that Gordo, Richard Anderson, David Neelham and others have discussed it.
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As to actually hypothesizing, I do wonder what US would incorporate into its fleet and system. Clearly, the demise of UA would create a big hole in the Star Alliance system. US can serve Europe to an extent - although not with the same amount of lift that UA has to Europe.
US has a total deficiency with regard to Asia. US''s one or two options would be to acquire the hub operations at either SFO or DEN. US would need long range planes to fly these routes, and I cannot begin to fathom what US is considering given that UA''s longhaul Asia craft are totally uncommon to US - 747s and 777s.