I was thinking at first that Frank might still be alive because they needed him to fly the plane, in other words, the island wasn't done with him so nothing will kill him until then. But my latest thought is that the ATL is everyone getting their lives back after MIB is defeated, so I think EVERYONE (with the exception of maybe Desmond, the constant) will die on the island. So now I think that plane isn't going anywhere and if I'm right, the island doesn't need Frank anymore (sorry Chesty!). The only way they'd still need him in the plot is if someone still plans to try to use the plane. Flocke was quick to dismiss it because 'there might be more c-4 hidden on the plane', but Sawyer and company might still be willing to take the chance if Frank is still alive.