
There's no reaction yet from Lufthansa, arguably United's closest member. United does provide Lufthansa with a significant amount of connecting traffic, and losing United wouldn't be good. Lufthansa has covered its bases in the US market a bit with last year's investment in jetBlue, but jetBlue can't give them anywhere near the same amount of feed that United can. Perhaps Tilton's comments might be meant to scare Lufthansa into making an investment in United (as it did in jetBlue) - in this case, United's ties with Lufthansa and Star would probably be stronger than ever.
Of course, all of this is assuming that United is actually serious about leaving Star. United will probably remain in Star as long as it is financially viable; if a better alternative arises, United will probably do the sensible thing and 'go for it', even if this means dropping in Star in favor of another alliance. (A United-Delta or United-Continental merger might mean that the airline could join SkyTeam, but this seems more likely with the former.) For United, the most important item on the agenda is making money, and if this means merging with another carrier and leaving Star, then a United-less Star could indeed be a possibility.