The war would probably have ended in 1945 anyway, but the battle for France in 1944 would have been much bloodier.
2. What would have happened if Kennedy had not gone to Dallas in 1963?
JFK would have defeated whoever the GOP nominee would have been. The Civil Rights Act of 1964 would have been passed, but the Great Society would have occurred more incrementally.
3. What would have happened if Lincoln had not gone to Ford's Theatre in 1865?
He would have been assassinated somewhere else, or he would have died of natural causes a la FDR; he was already showing the effects of being CinC during the war.
4. What would have happened if President Reagan would have replaced George HW Bush as his VP with a Conservative in 1984?
Impossible to tell without knowing whom it would be; there were very few true conservatives who would have had a power base of his/her own at the time. To have any effect, it would have to have been someone who came up through the ranks, not one of the rich-family mandarins, and in 1984 there weren't many such people.
Forgot one,what would have happened if the United States had not bailed Out Russia with material from the lend lease program?
Likely, and that nominee would probably still have been Barry Goldwater. I suspect that it wouldn't have been as massive as it was; LBJ got a lot of "sympathy" votes and besides, LBJ knew how to steal votes with the best of them.
Kennedy and Goldwater were friends from their days n the Seante. They had reportedly planned to have a whistle-stop tour together. They would stop in a given town and President Kennedy would explain his view on a given issue, then Senator Goldwater would rebut. At the next stop, they would reverse the order. Win or lose, it might have helped reduce some of the bitter divisiveness we see these days.
A lot of us in YAF wanted Jack Kemp to be VP, or possibly Phil Crane. Both were conservative members of Congress with a following, and both were noticeably younger than President Reagan. There were others, such as Gov. Pete DuPont, the "patrician populist", to whom Vice President Bush talked down in one of the 1988 debates. ("Pierre, let me help you.")
While still in office, or after his term had expired and he'd gone back to Illinois? Because those are two different scenarios.
The irony of it is that had Lincoln lived, Reconstruction would likely have been much smoother and less punitive. Johnson was trying to implement Lincoln's Reconstruction plan, but he had neither the force nor the political base that Lincoln had, so the Radical Republican under the leadership of Sumner and Stevens prevailed. They might not hve had Lincoln lived.