Last time we established that in the original history the Eldridge never returned, and commented that it made a difference in relation to Jimmy. Here the film is rather clever, possibly hedging its bets, trying to protect itself against making a mistake it could not foresee: Jimmy vanishes from the hospital, and it is the next day when Dave arrives at the Parker Ranch and discovers that his companion is alive, having returned to the past in the ship when it reappeared in the harbor.
We need to ask ourselves, though, what would have been the situation at the Parker Ranch if Jimmy had not yet returned to the vortex. It seems inevitable that he is going to do so; the fact that he did was presented as proof that it ultimately would happen to Dave as well, and therefore that Jimmy could not avoid it, would ultimately have been pulled back to the ship where he belonged. So whether he had already left for the past or not, if this is either fixed time or the final history of an N-jump, Jimmy will already have appeared in the past and been present at the ranch even if he had not yet departed from 1984. It is only a matter of whether our sensibilities balk at the notion of Jimmy meeting his future self when he has not yet traveled back to become part of that history; that part is irrelevant.
However, the part that is not irrelevant is what happens in the original history. Remember, the Eldridge vanished, and probably does not reappear until Dave returns and deactivates the equipment. Jimmy has left 1984, but is presently lost in that vortex waiting for Dave to return. Neither he nor anyone else can appear in what is still the original history, the extension of the version of events we explored last time.
This is a bit unusual. Normally when anyone leaves the future headed for the past, they create an anomaly that extends from the moment of their arrival to the moment of their departure. Jimmy has left the future headed for the past, but he has not yet arrived in the past. In a very real sense, he is sitting in the time machine while Dave continues exploring the future, and does not actually make his trip to the past until Dave takes him there.
Thus when Dave reaches the ranch, the elderly Jimmy is not there; the ship never returned. It was the Parker ranch, and Jimmy's wife Pam was pregnant when he vanished--the Navy will have said he died while involved in a top secret mission, and awarded him a posthumous Purple Heart. The Parker family will take in the widow of their son and their grandchild, so they will be there, and probably will inherit the ranch. However, they will never have heard any of the stories of Jimmy and Dave traveling to the future (and so will never have disbelieved), and they will not be prepared for a young man claiming to have leapt forward through time, looking exactly like Jimmy's friend of decades before, and claiming that only he and Jimmy escaped the ship, and Jimmy died of the effects of the field yesterday in a hospital in Nevada, disintegrating in the presence of the medical staff.
It will not affect the military's search for him, so he will still be running. However, it does impact his expectations. Jimmy disintegrated; the same thing seems to be happening to him. He can try to outrun it, but he does not know whether he can. It may be inevitable.
It is likely that he will make the decision to go to the base where he has heard Doctor Longstreet was conducting another experiment, to see whether the doctor who got him into this can explain what is happening. And so he comes to the place where they will ask him to don the suit and enter the vortex. They cannot, this time, tell him that he has already been seen doing it; they can only tell him that his only hope to escape the power pulling on him is to return to that ship and stop the generators.
It seems a convincing argument, and even if he does not agree, he is now close enough to the vortex that it will probably catch him before he leaves Nevada again anyway. One way or another, he will return to that ship.
What, though, if as we suggested was possible the ship actually does reappear, entirely by its own system failure, some time in the past? That makes it complicated, enough that we should look at it next time.