The view from the United States seems to have been that Diệm was a bumbler who was embarrassing the United States, alienating his own people through his abuse and governing through patronage, and consistently not winning the war despite his pledges. This is why, when there were reports of the ARVN generals speaking of coup (not unprecedented, since there were discussions of coups beforehand that never took place, and attempts before that took place and failed), the US pledged to them that it would still support South Vietnam whether or not the coup took place. It did take place.
However, the execution of Diệm and his brother came as a surprise to the United States, and was the worst case scenario as it was hoping he would simply be removed from the government and exiled, and not assassinated. The people involved in the coup had also promised Diệm, as the coup was underway, that if he surrendered they'd send him into exile. Instead, he fled his palace only to be caught up to later. He was given the same pledge and surrendered, but in custody both he and his brother were executed.
But what if, like many leaders before and since, Diệm had indeed gone into exile, whether by the generals keeping their word (which they may have if he surrendered at the palace and saved them that embarrassment) or he managing to somehow escape?
However, the execution of Diệm and his brother came as a surprise to the United States, and was the worst case scenario as it was hoping he would simply be removed from the government and exiled, and not assassinated. The people involved in the coup had also promised Diệm, as the coup was underway, that if he surrendered they'd send him into exile. Instead, he fled his palace only to be caught up to later. He was given the same pledge and surrendered, but in custody both he and his brother were executed.
But what if, like many leaders before and since, Diệm had indeed gone into exile, whether by the generals keeping their word (which they may have if he surrendered at the palace and saved them that embarrassment) or he managing to somehow escape?