Cembiten departed with Jeremiah in Session Nine: The Wilds of Isslyra
First appearing as an ancient silver, tailless, Dragonborn paladin, Cembiten’s gender was undetermined, and they use he/she/they indiscriminately, as if their own gender is of little consequence. In their long life, Cembiten served as a paladin for Tophor, and aided the fight against Vorugal (admittedly, they were late, a fact they ruefully confessed). Over time, they knew both Vox Machina and had opportunity to travel Exandria before returning home to help the founding of Ravinia.
When the Civil War began, Cembiten was on the side who asked the mages to not make the city-island fly again, citing the dangers of such powerful magics and expressing doubts as to the ultimate intentions. When this broke down into war, Cembiten did their best, but in the end it was their release of the imprisioned Emror that turned the tide against them.
Surviving by luck alone (or perhaps the protections of their ancestors), Cembiten retreated to the Ravenite caves (the same ones Vox Machina spoke to Tofor in, many years before), and bided their time. At the urging of their ancestors, Cembiten wrote the history of Ravinia, the war and everything, including the vision they had of Flora (which was exact down to the dirt smears she had on her person the day they finally met). Cembiten understood their new goal was to survive and wait for Flora, to ensure she reached the location she was meant to, in order to save her people.
Cembiten promised to protect and aid the weary lost travelers, help them defeat Emror, and get home.
They actually managed to do so, casting the spell with the bards to return home, and turned themselves back into a relatively young dragonborn. Cembiten and Jeremiah left with Cembiten’s cousin, Vlad, to rejoin the Ravenites and share their stories.