Here's a hope against hope.
Desmond sets his boat in one direction for two weeks and can't get away from the island. He says they're stuck in a snow globe. There is also an idea that the Island floats.
What if this holds true not just horizonally but vertically? Maybe the sub will hit the bottom of the bubble and end up somewhere else, resurfaced. Frank, Sun, and Jin will hit fresh air.
I know... hope against hope. But this show is crazy.