Yes JFK would likely still campaign in Texas, but in Dallas, on a date and time and in the location where he would have to be for Oswald to successfully shoot him? That's much less clear. It's possible any campaigning in Dallas is postponed or done earlier. Maybe Oswald can't make it. Maybe Oswald gets caught for attempting to kill Gen. Edwin Walker earlier that year (he didn't get caught in real life, but a butterfly effect can change many things) or gets in some other kind of trouble. Maybe he picks a different target (his widow Marina actually said he wanted to kill Richard Nixon). Maybe he has a change of heart at some point, becomes less political and violent. Maybe JFK doesn't take the same route under the Texas Book Depository or doesn't do a motorcade at all, just has some kind of speaking event instead. Hell, maybe he does events in Houston or San Antonio or something instead of Dallas.
And that last part matters more than you might think, because according to maybe the only person to ever know both JFK and Oswald (as well as Marina), Priscilla McMillan, Oswald likely would not have shot JFK had he not taken the specific route under where he worked:
And the president came to him. Compared to the route, no other determinant mattered at all. Everything that had ever happened to Lee Oswald could have happened it exactly the way it had, his whole life could have been exactly what it had been, and it would not have made any difference. President Kennedy could have come and gone from Dallas in perfect safety. But the choice of a route that would carry the president past his window could mean only one thing to Lee—fate, duty, and historical necessity had come together in this time and place and singled him out to do the deed.
The tragedy of the president's assassination was its terrible randomness.
In other words, that specific route made Oswald feel like it was his destiny to shoot JFK. Any even slight deviation and there is a good chance he never would have attempted it, as she does not seem to believe he would have gone out of his way to kill Kennedy, that it was essential that he come to him.
You also have to remember that part of the reason Kennedy was in Texas at that time was to help assuage tensions between the liberal and conservative wings of the state party; it wasn't just a campaign trip. LBJ's death might have helped alleviate those tensions earlier, and JFK might not have campaigned there until later in 1964. Or he might have been there earlier for LBJ's funeral, and wouldn't feel compelled to go back again until later. Giving plenty of time for other things to butterfly Oswald's shot away.
All this is to say I think it's highly likely that the assassination is butterflied away. And even if it's not, maybe JFK appoints someone else as VP first, so whoever that is becomes President instead of McCormack. True, LBJ didn't bother to appoint a VP until he and Humphrey won the election, but maybe JFK would if it happened nearly 2 years before the next election instead of less than 1.
Anyway, just assuming that JFK lives, I imagine he probably is able to successfully pass the Civil Rights Act and wins the 1964 election in a landslide, though maybe not as big of one as LBJ won in reality. (Although, the biggest reason Goldwater lost so badly wasn't because of a "sympathy bump" over the assassination as is commonly portrayed; it's because he was seen as an extremist, plus JFK was very popular.)
The rest is largely up for debate and is a pretty standard "What if JFK lived?" open question in regards to how Vietnam would have played out, how effectively he could have passed other legislation like Medicare, Medicaid, Voting Rights Act, etc. LBJ's legislative skills would certainly be missed. The biggest question in my mind is who JFK replaces LBJ with, whether before or during the election. I can actually see it being John Connally or Ralph Yarborough to replace LBJ as a Texan.
