So, Juliet said, via Miles, "It worked". Why was Juliet so wishy washy pertaining to the detonation of Jughead? I know that there's the obvious reason about Sawyer's devotion to Kate, but may I suggest something else about the "It worked" comment.
Maybe Jughead didn't create FST. Maybe it's sole function was to bring the crashies to the present day so that they could assist Jacob. Remember, her spirit said, "It worked" but not which part of "it" had "worked". Since an Island reset really shouldn't have brought them to present day unaltered, it is likely to assume that Juliet meant something else. Since they arrived in present day to help Jacob (and since Jacob stated "They're coming", implying he knew that Jughead would bring the crashies there), it might not be a stretch to assume that "it worked" because it brought the people to the present. From there, they can destroy MIB, and THEN reset history, creating a FST with the island sunk and everything safe. With MIB destroyed, there would be no need for the island, so it could be destroyed in the past (say around, o, I don't know, 1977?).
Was Juliet against the detonation until she realized that it had to happen to help Jacob? Is this something she only saw when she was dead/close to death?
This is a lot of guesswork and theory. :)