America could have continued to pour treasure rather than blood into Vietnam. The survival of South Vietnam is debatable. I would argue the nation became overly reliant on the U.S. military, hindering it's ability to develop and support itself as an independent, self capable nation. However, there was a reason it fell. South Vietnam was a perfect failed State. In every category, it failed. It was a mass Buddhist nation where Diem persecuted the majority. It was a nation that needed a strong military, which was instead rife with corruption and nepotism. The government was unstable, and the allegiance of the people was shaky. Diem was a terrible leader, but at the same time, he was arguably the better of the ones that followed. But it is like getting a cold when you are already terminal with cancer. And in truth, Diem was better only in terms of a stable government, without the period of revolving door generals until Thieu. Which is like saying a child is better with a two parent household rather than a single mother, despite the father being an unemployed, abusive drunk. How can that survive?