Let's think about this. Domestically, Delta and Northwest have come together to form a massive global airline. United (UAUA) and Continental (CAL) are sleeping together in their virtual merger. That leaves American and, well, US Airways (LCC) as the odd men out. While there's probably little surprise about where US Airways stands, American is more surprising. And it gets worse internationally.
If we look over the Atlantic, American is again the one in trouble. Continental, United, and Lufthansa have expanded into a major joint venture with antitrust immunity. Delta's joint venture with Air France/KLM also has antitrust immunity. That leaves American and British Airways (BA) still trying to get a deal together after years of being denied. The latest news makes it sound like they will still have to give up Heathrow slots, something they don't want to do. So they sit in limbo in this half-assed partnership. You can't even earn American AAdvantage miles when you fly BA over the Atlantic. And BA looks to be the weakest of the large European carriers these days.
Now we have a battle brewing in the Pacific as well. ANA, Continental, and United have already applied for a joint venture with antitrust immunity, and they will most certainly get it. If JAL chooses Delta, they will do try for the same. SkyTeam and Star Alliance will have strong alliances with joint ventures that hold antitrust immunity over both oceans. oneworld will still be a patchwork of airlines trying to pull something, anything, together.
And that is why American is fighting so hard to pull together this JAL deal. Without it, the alliance looks significantly weaker. Will the alliance disappear? I highly doubt it. Maybe Korean Air would leave SkyTeam and align with oneworld, but Japan is clearly the prize in North Asia. And they won't have a horse in the race if JAL leaves. They'll just be stuck trying to play catch-up.