Star Trek: Deep Space Nine Season 5 Episode 22

The DS9 cast discovers a small colony on a remote world that was originally populated by them 200 years earlier due to a time-travel accident with the Defiant. The current colonists lives depend on making sure that accident happens again, even though they’ve now forwarned the crew that it will happen. Each crew member needs to decide if they are willing to give up their lives on DS9 in order to preserve the history of the colony.