It seems like either: A) his body was never loaded onto the plane,

he was a ghost, or C) the island brought him back to life in the same way it made Locke walk again. Hopefully we'll find out at some point.
I wasn't sure if it was the tail or just a chunk of debris. If it is the tail, he might want to delicately mention that to the lady whose husband was back in the bathroom since she believes he's still alive on the island somewhere. Maybe he figures he'll point it out when they go to gather fresh water. I wonder what the significance is of the dolls. I guess there doesn't have to be, but I assume JJ put those in there for a reason. He plans his storylines out so far in advance I always think he carefully foreshadows things.