We got to know Ellie during her final days. And while we are having a memorial here in here honor, we really have no idea how she met her end. We know how her robot clone met its end, but Ellie's fate was never revealed to us. Ellie was snatched up by Cochran's robots, never to be seen again. We're told she's being kept in a room in the factory, but once rescued we find that she is one of the robots herself.
I'm sure some would argue she was a robot the entire time. While that sounds like an interesting and devious concept, it just can't be. Ellie's behavior does not change until the final act goes into effect. And none of the other robots had been noted to do anything other than robot behavior. Its also perfectly fitting of Tommy Lee Wallace and his script to just toss in an Ellie robot in the end without ever thinking of the probability of it. I know the plot of this movie is crazy, but its not to I Still Know What You Did Last Summer extremes where Cochran would create an Ellie-bot just to go hours south to lead the alcoholic swingin' carefree doctor who witnessed a robot killing someone knowing the secret that didn't diverge the secret up to the factory to have him investigate and try to expose you. It's too wild, even for Tommy Lee Wallace.
Ellie Grimbridge was a super cute sleuthy girl who had done most of her own investigation, but needed accomplice for fear of disappearing and no one knowing what truths she could uncover. Her only hope, Dr. Challis. While Dr. Challis kinda held up the investigating some ("Whoa, slow down! It's getting late. I could use a drink! Let's take our time."), he was an admirable partner. Plus, for reasons women will never explain, she could not resist the Atkins. While Ellie looked about 1/2 his age, she's claimed she was much older.
In, the end, Ellie...we'll never know what really happened to you on Halloween night, 1982. Maybe you're still out there. But this is a horror film franchise, so I'm going to assume the worst happened to you. Here's to Ellie!