We don't know when they all really died... it's left to our own imagination. We can assume the plane got off the island okay and made it home since they showed the people with smiles on their face knowing they were going home and Jack seeing the plane fly overhead... he knew he helped make that happen and did his job saving them. Hurley and Ben talked about being a good #1 and #2 on the island, so we can assume they lived on the island for some time after Jack died.
Everyone died at different times and we have no clue. They all came together once everyone died and entered "the light" as a group.
I was a little mixed at the final immediately after the show but the more I thought about it, the more I liked it. I didn't care about getting specific answers, but wanted to know more about life after the island and if everyone would make it back home.