Originally, most of the characters are in the process of dying or being treated at the crash site, Some of the characters are figments of some of the other characters' imaginations. The flashbacks are "their lives flashing in front of their eyes." If they die, they died or were "figments." Many are in comas and eventually they have been transported to the "Hatches" The hospital, but in their minds (they are still unconcious) they only see the island and are stuck with their most recent memories of the people who they sat near or met at the airport, etc.

Desmond is really a Doctor - working on Charlie (if he has anything to do with saving Claire - maybe she receives an organ donation from Charlie.

The End: We will see who actually exists, the emts and transports to the hospital, the recovery and deaths of our characters and the what the future holds (and how they were effected) after the crash.

Jack, being a doctor, after he is treated, will help work on the injured and help save those he can - after all have been treated or die - we see him in his flash forward...

Where are the children? Pediatrics.