He might have survived the first shot through the neck if he had bent over to lower his head into the car’s interior. The back brace prevented that and left him open for the head shot.
There's a book called "Conspiracy of One" by Jim Moore, in which he makes a very compelling case that the first shot was fatal (even as Kennedy had a few moments to reflexively reach for his neck).
Why would he have bent over? Like so many JFK assassination discussions this is just silly. While it’s not a supersonic bullet the time frame between the sound hitting his ears and the bullet hitting him wouldn’t even be long enough for him to think “gun shot” much less bend over.