The Dane sisters
In Uncanny X-Men #249 from 1989, the villain Zaladane surprised Lorna Dane (Polaris) by calling her sister. It appeared as if their family relation would never be explained following the death of Zaladane in Uncanny X-Men #275 in 1991, but it is possible that Chris Claremont had intended to revive Zaladane and resolve the issue. Certainly, Amazing Heroes #192 featured a design sketch by Jim Lee of Zaladane along with some for Omega Red, who at the time was set to debut in X-Men vol.2 #3 in 1991. With Claremont’s departure, the resurrection of Zaladane just ended up not happening.
Ten years later, in 2001, when Claremont left Uncanny X-Men for the second time to write X-Treme X-Men, Zaladane’s resurrection ended up not happening again: “Also lost in the shuffle: (…) a story in the Savage Land reintroducing Zaladane as a vengeful earth-oriented character, who manipulates tectonic plates the way her sister, Lorna, does magnetism, and her desire to avenge herself against Magneto (who “killed” her in Uncanny X-Men #275) by destroying Genosha (an island nation which Magneto ruled at the time),” Claremont revealed to Cinescape.com.
At the time, Marvel instituted an editorial policy against resurrecting dead characters, which may explain why Zaladane’s resurrection didn’t happen in the 2001-2002 X-Treme X-Men: Savage Land mini-series either, but Genosha did end up getting destroyed, although by Sentinels, in New X-Men #115 in 2001, written by Grant Morrison.