10 Star Trek Timelines That Were Erased

Children Of Time arrives in the later end of Deep Space Nine's fifth season. As the show was gearing up for the true explosion of the Dominion War, this was a little glance at what could be, if events went another way. The Defiant encounters a planet that is surrounded by a barrier - one strong enough to cause havoc with the ship's systems.

This leads to a crashlanding and a meeting of the minds that was, to put it plainly, unexpected. This was both the first time that the ship had arrived - and it was a long-awaited return at the same time. The barrier surrounding the planet was temporal. A settlement had sprung up, almost two centuries old, made of survivors - from the Defiant. 

In a spot of timey wimey hijinks, the ship was transported back in time when it tried to leave the planet. That time was devastating, leading to the deaths of several crew, and making the ship unsalvagable. Only Odo (and technically Dax, via the symbiont) survived to 'modern' day - which leads to this timeline's erasure. 

Odo, unable to lose Major Kira once again, uses the research that he spent centuries working on to ensure that this time, the Defiant escapes orbit. He saves Kira - at the cost of the entire settlement, and two century's worth of history.