Marc Guggenheim recently spoke to TVLine and explained that — while the original intention was to end the series with Oliver escaping Lian Yu — the creative team behind Arrow has decided not to go down that particular route.
Season 5 will end with Oliver escaping Lian Yu, and the show will move forward from there.
Although most of us had generally assumed that Arrow would come full circle over the course the series, that plan seems to have changed.
Those plans were initially put in place early in the show’s existence when the idea of a five season run seemed like a moonshot; now that Arrow has established a strong degree of popularity (and it will likely run considerably longer than five years) the writers have room to play with the story and deviate from the original plan.