As far as the island, we have to see how Slade loses his eye & why Ollie think's he's dead (Sara also thought he was dead). Remember his mask was stuck to a post on the beach in the first ep with an arrow in the eyehole. We also have to get Sara off the island and Ollie think's she's dead. I think she mentioned she was in Hong Kong when the Leage of Assasins found her.
Ollie also has to end up beind the only person on the island.

Actually, present day Sara once asked "what happened to Slade?" and Ollie refused to answer. So unless he told her offscreen, there's no reason for Sara to assume Slade was dead.