One of the biggest what ifs of American history, no doubt. Here’s my take:
-Kennedy wins re-election in 1964. This is almost inevitable as JFK had the highest average approval rating in Gallup history at 70% at the time of his death. He was still widely popular and definitely would have beaten Goldwater.
-Kennedy would not have invaded Vietnam to the same extent that LBJ did. His quote from NBC Sept 1963 reads: ‘its their war, they will win it or lose it’. He sent a few thousand advisors in but I don’t think he would have done a full scale conscription like LBJ and the Tet Offensive etc would not have happened
-Civil Rights legislation does not pass. LBJ is widely considered to be one of the greatest legislators ever and JFK did not have that talent. As a result, we can say that the South stays on the Democrats side for at least another decade. The riots of 1968 however, might have been even more consequential and MLK Jr would have been even more revered. Nixon would probably still win election against Humphrey.
-JFK lives to see his moon shot get fulfilled. Such a shame he never saw that.
-Medicare/Medicaid legislation I believe would have gotten passed as it was not as controversial as the Civil Rights bill. The same thing with the Immigration Act. The Great Society plans of LBJ half of it would still get passed I think, but with much more debate.
-RFK would still be alive. He would have probably not run until the 1970s.
tldr; or to take a quote of JFK “in the final analysis”, I think JFK surviving would have been better concerning Vietnam, but worse considering the Civil Rights issue.