Almost every theory that I have posted that has been removed has been removed by the same user. Coincidence? Fate?
Ben didn't die when Sayid shot him because he couldn't die, because he definitely lived to become adult Ben. Whatever happened, happened. Jacob met Hurley just hours before Hurley boarded the Ajira flight, yet was able to return to the island in a similar time, without the need for the Ajira flight. It seems to me that it's quite likely that he is able to travel through time in some way. There are hieroglyphics by the Frozen Donkey Wheel, and he lives in an Egyptian statue. It's not a huge leap. Given that, it's possible that the reason why Richard and Jack (and possibly others) can't die is because they will be present at a point in the future that Jacob has already witness. Whatever happened, happened. But as we haven't seen Jacob hopping inside a TARDIS, that theory should be deleted.
Widmore may have been able to find the island with Sun's help, perhaps with some sort of tracking device. The last time they spoke, Sun said that they had common interests: to kill Ben. Of course, mis-attributing that quote to Widmore instead of Sun fundamentally changes the dynamic of their encounter, so the theory that they're working together must surely be wrong and worthy of deletion.