Why do you think JFK authorized on paper in Oct 1963 the withdrawal of 1000 military personal by the end of 1963? To help him win re-election the following year rather than genuinely being sure the US would be pulling out of Vietnam in 1965?
The withdrawal was, in my view, to put pressure on Diem to change his policies on the Buddhists. The plan to withdraw troops over time was always contingent on the ability of the South to take on more of the war. The US would draw down as the South ramped up its efforts.
The question then was what would happen if the South couldn't ramp up those efforts? RFK answered that question in 1964. Well, not directly:
Question: "And if [the South] Vietnamese were about to lose it, would he [JFK] propose to go in on land if he had to?
Kennedy: "Well, we'd face that when we came to it."
In November of 1963 they hadn't had to face that yet.
RFK also said this about the war:
Question: "What was the overwhelming reason [for our support of the South]?
Kennedy: "Just the loss of all of Southeast Asia if you lost Vietnam. I think everybody was quite clear that the rest of Southeast Asia would fall."
Question: "What if it did?"
Kennedy: "Just have profound effects as far as our position throughout the world, and our position in a rather vital part of the world. Also, it would affect what happened in India, of course, which in turn has an effect on the Middle East. Just, it would have, everybody felt, a very adverse effect. It would have an effect on Indonesia, hundred million population. All of these countries would be affected by the fall of Vietnam to the Communists, particularly as we had made such a fuss in the United States both under President Eisenhower and President Kennedy about the preservation of the integrity of Vietnam."
Question: "There was never any consideration given to pulling out?"
Kennedy: "No."
I don't think that was RFK engaging in public relations or blowing smoke. The Pentagon Papers and the biographies of McNamara and Rusk show this was true. There was no consideration at that time to simply leave.
Full RFK interview here:
http://mcadams.posc.mu.edu/vietnam.htm