It's conflicting.
It's stated that she died atop Mount Kilimanjaro watching prehistoric humans flourish, but it's said again by Chakas/343 that she's still alive.
It's just one of "those things".
Last we heard, the Librarian was on Earth. She had learned three things:
1.) The Domain was the Organon
2.) The Domain was protected in Precursor arcitechture
3.) With the Domain gone, her husband would be left alone for eons, with nothing but his rage!
It is possible the Librarian sought to save the Domain or left on some other unknown mission. There was something she needed to do before dying, which meant she had to survive the Halo Activation. She may still be out there and 343GS could have figured this out after years of thinking.
I don't know what to believe about this lady. Half the time she's dead or somewhere's no one knows but I hope she's alive. I would like to see more living forerunner and I think she'd be a good character in the plot for later games. Her appearance was pretty brief and if you don't follow the books or other media, you'd have no clue what was up with her. Maybe there could be some kind of level or whatever in a later game where the main character joins Spark at some point on his quest to find her. I dunno.
Personally, I find The Librarian as a very interesting Forerunner or person with a great background or backstory. I would like to know more about her, and I hope she is still alive. The Ancilla on Requiem actually got me excited.
It annoys me how she cared more about the humans than the mantle when it was already broken, I feel sorry for the ur didact coz he had the shield worlds all set up
The Didact was insane, he tried to turn all humans into mindless robots as his army.
Chakas/Spark never stated he knew where the Librarian is, rather he said he knew where the "Lifeshaper" is. By then end of Silentium the last Lifeshaper after the Librarian was Chant to Green. Chakas/Spark may be referring to Chant to Green rather than the Librarian so it's likely the Librarian died after that activation of the Ark and Chant to Green is the Lifeshaper Spark is after. Still, we can always hope.
She decided to die from the halo rings so that her heir can take her place as the new librarian, her heir is named Chant-to-Green.