10 Star Trek Characters Who Died Off-Screen
8. Ben Sisko (Mirror)
This one's in a similar vein to the "is he, isn't he" Lorca Factor but the opposite way round.
Deep Space Nine's second season episode Crossover dropped Kira and Bashir into the fabled Mirror Universe for the first time since 1967's Mirror, Mirror. A lifetime of changes had seen the Terran Empire fall and the rise of the Klingon/Cardassian Alliance. Kira is now in command of Terok Nor as the Intendant. Among her minions is one privateer Ben Sisko. That Sisko would swap sides and assist Kira and Bashir in returning to their universe. This would be his only appearance.
By the time that viewers took a second trip Through the Looking Glass, the Terrans needed Prime Sisko to step into the place of their Ben, following the latter's apparent death during an attempt to convince his estranged wife to leave Terok Nor.
While his ship was destroyed and lost with all hands, there's still no absolute proof of his demise. This means one simple thing - Mirror Sisko is still alive and well, potentially sipping jippers away from the front lines of the conflict.