Leaving Desmond-Lost Finale

They can't stay with Desmond because he wasn't a member of Flight 815. How would they explain Desmond and Lupitis (sp) when they were supposed to be on the dingy from the plane sort of lost at sea until they came upon that island? As far as everyone else is concerned in the really real world, that plane was found at the bottom of the ocean and, they were the only 6 that survived which means that they couldn't have just come across Desmond and Lupitis. Also, Penny's Whitmore's daughter and, I think someone knows about Whitmore in that group so, that could be very dangerous for them to have been found by Penny. And, since Desmond has been missing, it would bring to light an island that no one is supposed to know about. So, it was for the best that they were nowhere near Desmond when they were rescued.

Penny is in danger, as Ben wants to kill her after Penny's father had Ben's daughter killed. There is no way they want to be found. I think the story is weak, but its the only one that Jack could come up with quickly to protect everyone else on the island. Sawyer swam to the beach and Juliet was sitting on the beach, so were alive on the island. We know "Others" are still there also.

They can't stay with Desmond because that was Penny's boat (ironic :D) and since Penny is Widmore daughter she and Des are hiding from him so they don't want to have a place in the rescue story. They went in an island near the place where Widmore faked the incident and they will tell at the people who will find them that after the crash they lived in an island near that place (see press conference explanation in episode 12).