It could bring the whole narrative full circle. If Ellie's story ends in a way that ties up loose ends from the beginning, it'll give a sense of completion. For example, if her journey started with a search for something (like a cure or a sense of purpose) and ends with either achieving it or realizing it was never what she really needed. It'll have a huge impact on how we view the entire story.
The end of Ellie's story might shift the focus of the overall narrative. If she has a major role in the end, like making a big decision that changes the fate of the world in the game, it could lead to new stories or interpretations. It might also make us re - evaluate other characters' roles in relation to her. For instance, if she becomes a martyr, it'll make us think about how other characters will carry on without her and how her actions influenced them.