I don't think LOST took back the death really. Keeping in mind that Locke told Boone he'd free himself given the proper motivation, I suspected island strangeness was going to come into play. Then when Shannon cried out to Boone to rescue her because Locke had also kidnapped her and tied her up, I suspected the whole thing was a hallucination. We never once saw Locke make any kind of moves toward kidnapping Shannon. I imagined if he really had done so, the writers would have given us something (like Locke approaching Shannon, giving her an evil eye, following her on a stroll in the jungle...something).

Something also tells me that if Shannon really had gotten taken and killed by the beast, there wouldn't be an entire corpse laying around for someone to discover later on.