Contrary to what
@Slime_blob said, I sincerely doubt that the American state department and intelligence state is going to “destroy the commie rebellion” through prosperity, democracy, and stability. OTL showed us that this policy is a path with very slow returns (despite proven success), and losing both Korea and China will put an immense paranoia on Asian Policy. I strongly doubt the resulting policies will avoid dictatorship, in fact I think it will double down on dictatorship as the best means of warding off communism. Say what what you will, but strongmen, when given strong American backing and tools, did provide results (Suharto, Syngman Rhee, Pinochet, Armas, the Brazilian junta, Trujillo for a time, the Shah’s Iranian government, and a slew of others). Not to mention, not explicitly autocratic but at least meddling with democratic processes to ensure results like the eternal rule of the Liberal-Democratic Party in Japan. It’s wishful thinking to say that the American foreign policy departments, with the kind of people who staffed them at this time, are going to sit back and realize that they need a slow plan of investment and stability to ensure proper allies. They’re going to favor decisive action and results, which unfortunately means strong anti-communist dictatorships that slaughter their indigenous left wings (because, after all, that strategy mostly worked).
We’ll be left with military cliques ruling the rumps of Taiwan and Jeju Island, a more militarized Japan with stronger funding and co-ordination between American intelligence and the Japanese right, we’d probably still get Marcos for the Philippines, there would probably be continued shenanigans with Operation Paper and the Yunnan Anti-Communist National Salvation Army in Burma and their opium trade to finance operations, and American military investment into Indochina will be pouring in.
I don’t see a future in which the name of the game for American policy in Asia is slowly building functional and truly democratic systems over the course of decades, it will be intense anti-communism resulting in entrusting political systems to the the indigenous right and/or radical right to keep a lid on things while the American military is deployed when it feels it needs to be. The OPC and then CIA will continue to oversee opium production and smuggling in the Golden Triangle to raise money for these regimes, and South-East Asia will be of particular interest to Washington and more resources will be devoted to the area than IOTL. Things look unfortunate for everyone in this alternate timeline...