Good catch Mango. The "Oceanic Six" must have returned to civilization by conventional means.
This leads me to speculate that perhaps Sayid, Desmond and Michael are joined on the freighter by Jack, Kate, Hurley, Sun and Aaron and they return to the world, perhaps via Fiji. It could be that this group of five make up the load limit of the helicopter and are chosen by some process of negotiation or chance that we don't yet know and that for some electromagnetic or mechanical reason or threat situation only one flight is possible. They are sworn to some pact of secrecy to preserve Ben's precious Island for him and/or to keep him from killing their friends.
At Fiji, Des and Michael could be separated from the others before they are revealed to the press as the "Oceanic Six". Des is then free to take Penny to whatever protected place Widmore believes her to be safely living until Ben comes to get her (or sends his agent, Sayid). Michael could go to L.A. to live alone and miserable under an assumed name until his death and solitary burial via the Hoffs/Drawlar funeral home.
Of course, why those additional five are chosen will make for some interesting drama, as will the outcome for the rest of the Losties, especially Claire and Jin who, if they live, are separated from their loved ones.
This is why I love Lost. The show allows and encourages the audience to think creatively along with the writers.
I like these speculations. Now, I'm trying to figure out logistics. Before, Frank said he could only take three people, which turned out to be Des, Sayid and Naomi/the piece of meat. However, that was only because his fuel situation was low. That doesn't mean in the future the fuel will again be so low, hence, more people might be able to go back. The flight bringing the mercs showed that the heli can convey up to six people. So, a complement of passengers returned to the freighter by Frank could include:
1) Sun, who is pregnant, and can't stay
2) Jack, our intrepid leader
3) Flirty, nosy Kate, who convinces Jack to let her come over Juliet (Game: Kate!)
4 & 5) Hurley, who's weight is such that he had to buy two tix to board Flight 815 in Sydney
6) Claire, who boards the chopper, but dies later on the Freighter, somehow due to a decision Jack makes
6a) Aaron, who weighs so little, doesn't bear upon any weight-limit considerations
Thus, Sun, Jack, Kate, Hurley & Aaron join Sayid on the freighter, and become the Oceanic 6. I think Des is kept in play, for a later confrontation with Ben in defense of Penny.
