After some thinking about the show last night i have some ideas
I think Sayid being escorted is obviously a Ben or Widmore ploy to get him onto the plane.
I think that Kate gave Desmond Aaron so he could bring him back to the island via boat. She regrets bringing him back to the island but would not risk him in a plane crash.
I think that the plane did not crash but rather that Oceanic 6, Ben and Locke were teleported off when the white flash happend. I think Frank and the lady escorting Sayid and that guy who talked to Jack are also now on the island.
I have a feeling that the “incidend” that all the Dharma people talk about is the Losties using the donkey wheel to get back to their proper time line.