I posted this same theory on someone else's message page, but I am hoping to get a little more feedback or thoughts on this. I also got a little confused on this Wiki site, so forgive me if you see this more than once, I just joined last night!
What if the bomb did go off, it just had different outcomes than what Faraday predicted. They woke up in present time on the island, and maybe that is what Jacob meant when he said "They're coming" in the 5th season finale. The "losties" are coming to present time. I don't know exactly what their purpose is on the island, but I do know that the MIB wants to go "home", wherever that is. Possibly their mission is to (for some reason) help MIB go home.... once he goes home, and now that Jacob is dead, there is no one there to rule it, hence the island will fall apart. Or sink perhaps? Possibly something else happens to erase everything that happened to the people on the island, therefore the different lives and alternate timeline we are seeing now. I think the alternate timeline could possibly be what would happen to these people if the island was gone, or sunk, so to speak. If there is no island to crash on, there is no big island mystery. Maybe in this alt. timeline, Jacob didn't come to those certain people, therefore not destined to be on the island. Little do they know ( or maybe they do!) that they DID go to the island, but through time traveling (due to the island) everything is erased, reversed, changed, etc.
This is just something to think about, if it could be a possibilty. Of course at this point, what ISN'T a possibility? It does sound crazy, yes. But isn't time travel crazy to begin with?