Just my random thought...well not too random cause its about LOST on a page called Lostpedia.
Maybe anyone who dies ON the island is stuck in a time loop as a result. Anyone who dies OFF island is not stuck in a loop.
Then I go on to say...
Ben and Sun DO NOT die on the island. Hurley, Kate, Sayid, Jack, and many others (JACOB) DO die on the island. As such they are stuck in a loop.
This is why some people go back to 77 upon return to the island, and some people dont. Its all about where they die.
Now lets talk about John Locke... He was gonna die off island (no loop) after getting shoved out a window, but Jacob saved him and he came to the island. John Locke dying on the island is what Jacob wants.
He was gonna die MANY times on the island, but things happened to prevent that. Actually I think that over time(s)/loops, Nemesis learned what was killing Locke and cultured Locke so he wouldn't die.
a) He was gonna climb into the Beachcraft which was gonna fall and kill him, but Nemesis busted his leg so Boone went instead (id rather think his leg issue was a result of Ethan shooting him there emanating from a different time - oh well) b) He was gonna get shot by Ben and die in the DHARMA pit, but Nemesis coerced a situation where Locke had his kidney removed so he wasn't mortally wounded. c) Oh theres more...but I bet Nemesis was saving Locke every single time (poor John thinks its he who is so special...)
Then Nemesis made sure Locke was going to die off island, so he wasn't in an island Loop. I will call this...a loophole (even though really...i think its more to do with the compass somehow).