Kai Opaka (played by Camile Saviola) appeared in the first episode of Star Trek: Deep Space Nine, in what looked like a fairly important role, but was then written out in her next appearance (‘Battle Lines’).
Whilst this set up the succession storyline, it seems a bit odd. Did Saviola get another job? Did the writers have a change of heart? Or was her exit planned from the pilot? I haven’t been able to find any reports of what happened there.