If history isn't recorded the terminator (or whoever gave it it's task) won't know what it should be sent to do.

Actually, this is a GREAT question, and the answer is actually quite simple: YES! for as the Terminator erases or changes history, those historians who specialize in certain fields or certain personalities, simply cease to exist. THis sudden and inexplicable disappearance opens up tenure-track positions in universities and think tanks throughout the world and a premium - usually in the form of a signing bonus - is considered appropriate for event he most mediocre of historians. The Universities do not begrudge the money spent upon signing bonuses because, in the long run, it is actually cheaper than paying for tenured professors throughout their career: assistant professors, associate professors, full professors, professor emeritus, and full lich professors who can only be removed from their offices through an exorcism by an old priest and a young priest...but that's more a matter for /r/AskReligiousProfessors than history.

Nonetheless, many in the history community welcome out time-traveling robot overlord for without him, we'd have universities stocked with over-qualified, under-paid "adjunct" professors stuck in dead-end jobs, hopping from one university to another in order to make what a Kindergarten teacher makes in a year. Imagine how horrible that would be...

Ah, so, to return to your question, Terminators are good for business.

Due to the specifics of time travel in this Terminator-laden universe, temporal shenanigans do not actually change the history we experience. Previous timelines are not maintained or remembered by anyone except the time traveller.

So, aside from the testimony of one man and a robot, there may as well have been no time travel in 1984. History as we understand it is unchanged.

The Terminator doesn't actually change history. He creates paralell Universes.

The reason we know this is, in the Documentary Terminator", we see Kyle Reese go back in time and protect Sarah Connor from the original Terminator. Kyle Reese is sent by John Connor, the son of Sarah Connor.

Later on we see Kyle Reese and Sarah Connor have sex and it is strongly implied that with this act he fathers John Connor. The John Connor who sent him, can't be fathered by him, as this opens up an impossible paradoxon. Therefore we have to think that the John Connor that originally sent Kyle Reese must have had another father.

So we have timeline A -> Sarah Connor and John Doe have a child, John Connor, who leads the resistance and sends back Kyle Reese to save Sarah from the Terminator.

Then we have timeline B -> Sarah Connor and Kyle Reese have a child, John Connor, who delays the apocalypse by destroying the saved Terminator-parts together with Skynet creator Miles Dyson and a terminator sent by John Connor (who is Kyles son).

Therefore it is impossible for John Connor from timeline A and John Connor from timeline B to live in the same universe. Therefore we need to accept that both exist, but in different universes.

There is currently no known way to travel between these various universes.

edit: And to come back to your original question. History doesn't change, we just have to accept that our history isn't consistent for every existing parallel universe.

This seems more like /r/askphilosophy to me.

As historians our role is to simply record what had happened at the time of the writing. If what happened in the past is changed by future time travelers into that past, our work still has value of as a record of the former past. I can't get all existential about what might have been going to have been.

It is a great question, and perhaps we should view it the same way our military historians and battle commanders now view history based on our commander John Connor's position that history IS the battlefield and is continually being fought as we speak. As we continue our current military strategies of war against Skynet, we must assume that battles that take place in the past are actually still being fought. We must allocate resources chronologically the same way we allocate resources geographically. Even though our skirmishes seem to be taking place in the past, they are actually ongoing because each side is allocating resources to certain times and changing the outcome. Until the outcome is certain (if it even ever can be), we must assume the skirmish is ongoing, even in the past.

There are generally two different theories on time travel: Single timeline or infinite timelines.

In a single timeline, travel involves leaving the timestream, then rejoining it at a specific point. This means you can affect your own fate, like Fry being his own grandfather.

In Infinite timelines, travel involves bending your own timestream back on itself into a "loop", hence the name of the movie "Looper". In this case, timelines self correct; thus, if you try to be your own grandpa, your bio grandpa would adopt your bastard or your loop would cease to exist and you would vanish before orgasm.

As we know, based on the Terminator series of documentaries, the likely answer is the infinite timestreams. The reason historians track ever changing history is that records can be stored outside the timestreams and retrieved at a later time (how do you think we gained access to the documentaries in the first place?).

Looking at the sales of the documentary sales, there is a money as well as fame to be gained; as a single one of your parallel selves doing well can ensure the success for all!

At the end of the day, you shouldn't trust the historians, as they have much to gain, but continue to view all such documentaries and come to your own conclusions on the validity of yourself in this timeline. Rise up and better yourself to help yourself.