You were mentioning that everything stays the same as in real time except that JFK selects Senator Humphrey in 1960 instead of LBJ. Generally, Humphrey, being on the democratic ticket, would still win the 1964 election with the main reason being a contiuation of President Kennedy's policies, just like it happened in real time. But... you mentioned that JFK still dies. The question is "Does he?". With Humphrey as his vice president since January 20, 1961, there would be no need for Kennedy to go to Texas and try to attempt to "mend the democratic fences in Texas", as he had to do with LBJ on the ticket. Senator Johnson would still be majority leader in the Senate, and seeing that it was difficult for President Kennedy to get any of his agenda passed in Congress, it still would be with Johnson still in the Senate. With Humphrey as vice president, President Kennedy would not have been in Texas on November 22, 1963 and that date would not be a historical one today.
For these scenarios, you shouldn't think too deeply into them. Let's just say that Kennedy is assassinated in 1963.
