I knew when I was writing "need" that someone would jump all over that.
Of course no one actually needs Terminator or any movie for that matter. This is "need" in the artistic sense meaning that a work either does or doesn't need something to be complete.
I knew exactly what you meant by it, and it is that need I am disputing. Terminator didn't need T2 to be complete, it was a complete piece of work in it's own right, and T2 sure as hell didn't need T3 or T4. Surely each piece of work deserves to be judged on its own merit?
The "need" in the sense that you describe it will be defined by the film itself, not by other films. I've never understood this aversion people have to sequels or reboots, a good film is a good film, who cares what came before or after it.