The only difference this would make is that Adlai Stevenson, instead of Hubert Humphrey, would serve four years as Vice President of the United States.
In the election, Johnson/Stevenson win a landslide victory over Goldwater/Miller.
The Democrats do not nominate two time Presidential loser, big loser, Stevenson, as their Presidential nominee, to lead them to defeat for a third time. He would be a Vice President not successful in winning the party nomination, if he even ran for it, which would be very, very doubtful. Stevenson died in 1965.
Johnson/Stevenson 486
Goldwater/Miller 52