In the acclaimed Star Trek: Deep Space Nine episode "The Visitor", Ben Sisko is killed in an accident prior to the Dominion War, before Jake Sisko resets the timeline.
However, the episode takes place on Earth in (I believe) the Louisiana bayou, and Jake is living what appears to be a comfortable normal life, as is his young visitor. Flashbacks to visits to the area around DS9 in later years do not show Dominion conquest.
However, in the main timeline shown in all the subsequent episodes of the series, the Dominion come extremely close to a complete conquest of the Federation, and, indeed, according to the brilliant genetically engineered savants seen in later episodes, are statistically overwhelmingly favoured to do so. The show seems to indicate that it was only Ben Sisko's heroism, genius, and sacrifice that allowed Earth, let alone Bajor to escape.
Obviously, in real life, those episodes hadn't been written yet. But, in universe, why was Earth fine in the absence of Ben Sisko's brilliance, which the later seasons depict as absolutely crucial? Or was he actually just replaceable?