Lost Gallifrey (The Taking of Planet 5)

One duplicate Gallifrey was lost during the Battle of Mutter's Cluster, bringing the count down to nine. (PROSE: The Taking of Planet 5)

Behind the scenes
Within the novel The Taking of Planet 5, it was altogether unclear whether this Gallifrey was utterly destroyed, or if it was "lost" in a similar way to Ardethe or New Alexandria.