If that's headcanon, I think its pretty damn close to the strong implication of what's shown on the screen. Jean didn't die. She transcended. And if we're to take the little bit of Easter Egg right at the end, still keeps enough of herself to be interested in her homeworld.This may be straying into head canon, but the ending of the film felt a lot less tragic than the comics version.
The original storyline was really pure tragedy - Jean realized she was unable to control the Phoenix Force and killed herself to prevent a repeat of the destruction that she’d caused under its influence. (Of course, that was retconned considerably six years later.)
In the movie, Jean sacrificed herself to destroy Vuk and save the world... but I don’t think that she actually died. Instead, she successfully controlled the alien force, merging with to create a new entity. That moment was essentially the fulfillment of both “My emotions make me strong” and Charles telling her, “You can do anything you set your mind to.” Jean’s humanity tempered the power of the alien force and changed it into something that was no longer purely destructive.
I believe that’s symbolized by the hybrid entity assuming the form of the Phoenix, something the alien force had never done prior to that point in the film. Jean’s closing narration seemed to support that as well.