Remember way back in the first episode when the pilot, Seth Norris, told Jack and Kate that they'd lost radio contact and had traveled 1,000 miles off course. Then we know that Desmond failed to enter the numbers in time on Sept. 22, 2004, causing Flight 815 to break up and crash on the island.
So with that in mind, if Jack's plan works will they land safely in L.A. or will it be Fiji? The answer to that question lies in what caused the radio contact to break down. If they weren't near the island when their radio contact ended, then it's safe to assume that wasn't Desmond's work. After they lost contact, they flew 1,000 miles for 2 hours back toward Fiji and passed over the island as the Swan counter reached zero. The electromagnetic forces from the Swan broke up the plane and it crashed.
Many fans will say that the island caused the radio contact to break down, leading them to turn around and pass over the island. So if the Swan is never completed, will the island still cause the radio contact go down, leading the pilot to head toward Fiji? In that case, they'll land in Fiji since there's no Swan to cause the crash. Or their radio contact will never be lost and they'll end up in L.A., safe and sound.
But then again, what ever happened, happened ... so it's probably a moot point.
In other Lost news, there's a couple of things floating around the Web to hold fans over until the final season. Over at DamonCarltonandapolarbear.com, check out updates of art work about the show and other Easter Eggs. Also, at Comic Con Mysteries of the Universe Part 1 was shown. ABC's Lost site has release the second video (see below). Apparently this documentary will be part of the season 5 DVD set.