I think 1964 was pretty clearly a protest vote. The Deep South voted reliably Democratic downballot, and the other Southern states stayed loyal to Johnson. Don't get me wrong, Goldwater's campaign planted many seeds and obviously had an effect longterm, but I think the degree in which politics changed in 1964 is VASTLY overrated, mostly because such a narrative tells a nice, clean and easy story that fits into a textbook chapter quite nicely.
I'm not sure if 1968 was bound to have a third party, and I am also not sure that Nixon would have won any of those states without Wallace. History has (rightly) painted him in a negative light, but from what I've read, Nixon was clearly seen as a pro-civil rights politician during the time, despite his Law and Order schtick. I mean, enforcing the laws and cracking down on illegal protest (i.e., looting and vandalism), while possibly racially coded, is not even close to advocating for institutional inequality. Humphry was definitely not to the liking of most Southern Whites of the time, but I'm skeptical Nixon was viewed as much better. It's possible the South could have tried to give the same middle finger to HHH that it gave to LBJ, but the problem is its Republican alternative isn't anywhere near as palpatable. I think it's fairly undeniable that Rockefeller or Romney would have lost the South to Humphrey, had they been the nominee (think a similar result to Eisenhower minus WV, maybe?).
-No; Alabama also elected a bunch of GOP representatives. GOP candidates did well in the Goldwater-voting parts of the South when they ran and were credible.
Yes; a third party run was probably inevitable in 1968.
