Say that Humphrey doesn't run and so instead Gov. John Connally runs with the support of Johnson and the Democratic establishment. Meanwhile, Nixon isn't persuaded to leave retirement, and so Nelson Rockefeller wins the Republican nomination with the help of the GOP establishment. George Wallace does not run and endorses Connally. Connally picks "law-and-order" LA mayor Sam Yorty as his running mate, while Rockefeller picks Spiro Agnew (remember that at the time Agnew was considered a liberal to the left of Nixon, and he was a supporter of Rockefeller at the convention IRL).
How would the election pan out? Would Connally retake the Solid South? How much of the North would he retain? What percent of the black vote would each candidate receive (remember that Connally opposed the 1964 Civil Rights Act)?
I would imagine the result would be something like this: