Ceridwen did hide Gabella, in the Bair of Lacuna. The Twenty One did act together to create a second wife for Nemed, who was given an immortal soul but a mortal body. They settled and started a farm on the site that would later become The Seven Pines, but were presumably long gone by the time the gods met there to negotiate the end of the Godswr.
Anesidora died early in the Age of Dragons. For all we know, Os-Gabella captured Nemed more than ten thousand years after that.
(For most of the history of the world Anesidora's soul languished in the Netherworld, unhappy that she alone has no divine birthright. Since her heart was stolen and taken into Erebus by Gosea the Dwindling early in the Age of Rebirth. She now exists as a dark draconic shadow under the sway of her heart’s possessor. Though she isn’t evil, she is destructive and manifests such sorrow that most enemies fall into despair when confronted by her.)
Junil holds to such a strict interpretation of the Compact that he has never allowed his archangel to return to Erebus proper. (Other archangels come and go from Erebus all the time.) During the time Sabathiel was actually leading the Bannor Empire on Erebus, he dwelt in a sort of small demi-plane connected to Erebus on one end and Junil's vault on the other. Its connection to the inner sanctum of the Halls of Sabathiel may have been severed by the injustice and lack of faith of his priests, causing Sabathiel himself to retreat back to his home in Junil's vault.