The Flash has already been playing around with all manner of timey-wimey stuff in its first season, and thats only likely to increase with the addition of other dimensions (hello Earth-Two) and Legends of Tomorrow further exploring the possibilities of time-travel. Barry Allen has travelled into the past on a couple of occasions now, and any events altered can lead to changes in the future. While this was pretty much all taken care of in The Flash, there was no explanation of any possible ramifications his time-travelling had on the characters of Starling City; as we know, they share a universe, so would there be any knock-on effect for them? There has been speculation online that this could tie in with Saras death, but another theory is that it may lead to another version of the Arrow also appearing in an alternate universe alongside a different version of Barry Allen, perhaps even offering a first look at the Green Arrow. Itd be a pretty big leap for the show, but the sort it may need to take at some point.