I'm not sure how much traffic TWA is generating on either the MSY-SAT evening flight or the SAT-MSY morning flight, but it seems to me that there are 2 schools of thought:
1) There is probably not enough local traffic in either MSY or SAT to support a flight from each to JFK. Which is obviously why they combine the two.
2) Your argument as to the financial viability of the domestic JFK routes makes total sense to me. They probably do break even at best, but what I would wonder is what would happen to the profitability of the various trans-Atlantic routes if they pulled the domestic JFK flights. Being that the domestic flights feed the int'l ones at JFK, I can't see the int'l flights staying profitable. All TWA would be left with internationally would be the local New York market.
As to TWA's MSY-JFK service, they run just the one noonish nonstop, and the return flight flight comes in during the evening.
I'm not sure that a sole MSY-SAT flight makes financial sense, but tag it onto the JFK flight, and it may just work.
A hookup with JetBlue at some point in the future makes good sense to me. With JetBlue's ambitious plans for the future, considering their success of today, TWA would be smart to investigate the possibilities.
Tom in NO (at MSY)
"The criminal ineptitude makes you furious"-Bruce Springsteen, after seeing firsthand the damage from Hurricane Katrina