UA might want to attract global capital but doing so requires changing laws. Not all US airlines have said they want it and some may very well be able to pull together the financing to acquire other carriers, in which the federal gov't is far less likely to allow foreign carriers a bigger share of US carriers. If LH acquires a stake in UA, it does nothing to solve some of the structural problems in the US industry because you still have the same number of dysfunctional airlines.
I think it is fair to say that the alliance between CO/DL/NW is not turning out to be quite what was invisioned nor will UA be any more happy w/ US when they have to deal w/ HP. I think it will be shown before too long that domestic alliances really don't work because each carrier is still competing for the same group of passengers. It's one thing to have an alliance w/ a foreign carrier but it's quite another to join forces w/ another domestic carrier.
I could easily see CO going w/ UA and DL w/ NW but the latter is much more problematic - and I'm not sure that UA's people are ready to play second fiddle to CO which is the only way they will be treated if UA combines w/ UA. I don't think NW and DL would ever voluntarily merge; it would only happen in bankruptcy since both have significant debts that make them unattractive as is.
The reality is that companies outside of bankruptcy have much more control over their destiny than those in bankruptcy. If UA emerges from bankruptcy as an independent company, they could easily be a long-term industry contender and could even be instrumental in shaping the future of the industry. As long as they are in bankruptcy, they are subject to the whims of the creditors in finding and approving an acceptable reorganization plan.