That's an awesome point!! Jack is fully the kind of character that becomes so tunnellvisionised (yea, its a real word...now) that he would fully cock things up. Locke does have a thing going with the island - and with the appearance of walt, it is easy to see that Locke would want everyone to stay on the island until they serve the purpose of why they were brought there.

If you take a look at the characters that are "dead" or have left (charlie, eko, michael, walt, boone and shanon) they all dies after serving they're "purpose" (charlie - put himself aside for another, eko - regained his faith, michael - became a father, walt - accepted his father, boone - let go of shanon, shanon - found and accepted love)

Does this mean that we are about to lose Sawyer?????