I think the island is going to be physically moved and not moved through time. If the island moves through time, the same problem will keep happening. The island will be in the same spot at a different time. If it is the future, Widmore would make sure someone would use the previous info on the island to find it. If it is the past, Widmore would figure where it is eventually just like he found it now. Physically moving it would mean guaranteed safety cause no one would know where it is.

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