The Island survives. At the church Ben and Hugo congratulate each other for doing good job's as no.1 & no. 2 running the island, and i'm guessing stayed there until their deaths. All of the people gathered at the Church are already deceased, and for some reason they all meet together (because what they did on the Island was the most important parts of their lives) before they transition on to the "next phase". Obviously some of the people in the Church had died before (Christian), and others later (Hugo, Kate, Sawyer, Ben etc.). Keep in mind that Christian said the place they were in had no now or where or when, time has no relevance. It appeared that the sideways timeline's purpose was to provide a "second chance" for the survivors to amend the damages and unshoulder their burdens in their lives before moving on. They were all dead, but each lived out real lives before coming to that place. Kate for instance told Jack she had waited so long, she left the island on the plane, but Jack sacrificed himself to save the island. Even though it's frustrating that many of the scientific anomalies and mysteries of the island are never answered, the depiction of death and the emotional reintroductions of each character with their most loved ones was extremely powerful. In the end the mysteries of the island don't matter, but the time each person spent there and interacted with each other depicts human nature at it's most basic and most important.