Let's just say that the isalnd does have some strange healing power...and certain types of people cannot die. Richard hasn't aged a day. Mikial said he guessed the fence wasn't turned to a leathal dose and no one blinked an eye, but why would you have a fence like that that could NOT kill a regulat person. When Locke turned him over, he certainly looked dead, although Locke and the others were somewhat distracted.
If Locke has "seen into the island" and believes it to be beautiful, and heard Phantom Jacob, then maybe he, like Mikial cannot die. The island won't let him.
With that in mind, could Mrs. Klugh/ Bea be one of them?