After giving Barry and Iris the surprise of their lives at the end of season four of The Flash, Nora West-Allen became a major player in season five. Played by Jessica Parker Kennedy, Nora initially presented herself as being unable to return to the future before presenting the real reason for her arrival in the "past" -- to help stop the Cicada, the one villain her father had never been able to catch. However, it ultimately turned out that Eobard Thawne had been manipulating her for his own purposes and in the season five finale, Thawne's machinations resulted in Nora fading from existence thanks a new timeline taking hold. It looked like the end for Nora, but that doesn't mean she'll be gone forever.
In a recent interview with Collider, Kennedy was asked about the possibility that Nora could return to The Flash and while she admitted Nora's exit was real, there are always ways to come back.
"With comic book characters, anything could happen," Kennedy said. "She's gone for now, but I think that there's always a way to bring somebody back, on a show like that, and I definitely would be happy to do something like that. But yeah, as far as I know, she's gone, for the moment."
While Parker is right that in comic book-related entertainment death or disappearance isn't always permanent, The Flash in particular is a show where those who are gone may not be gone for good. Thawne himself is a primary example of that, having himself been wiped from existence at the end of season one when his ancestor Eddie sacrificed himself, thus making it where Eobard couldn't exist and causing the villain to disappear much the way Nora did. Of course, Thawne found a way to come back from that. There's also the concept of the various timelines. If they really wanted to, Barry could go back in his own past to earlier in season five where Nora was still alive, though doing so would have major consequences -- such as what happened when Barry created the Flashpoint timeline after saving his mother's life in the past.
That said, even if Nora herself doesn't ever return, her existence itself may still play a major role in the coming "Crisis on Infinite Earths". Nora spent all of season five documenting things in her journal using a special time language that does not change no matter what happens to the timeline. That means that everything Nor had recorded in her notebook remains and, in theory, includes everything she knew about Crisis as it happened in her own timeline. This information could end up being very useful for the heroes when "Crisis" hits -- or could end up creating its own batch of issues should the event "correct" the Arrowverse as the event did to the multiverse in comics. Nora's journal would contain a record of everything that was lost, which could be a complicated situation all its own.
The Flash returns this fall on The CW.