Island Sank Slowly by Jhisc9999

I've stated before that the timeline change had to begin shortly before or shortly after the bomb to account for us seeing Ben and his father in the Alt and also seeing the Dharma structures underwater. I proposed that it was before the bomb for several good reasons: http://theoriesonlost.blogspot.com/2010/03/alt-predates-bomb-by-jhisc9999.html. But I'm rethinking that after hearing that Miles' father is alive in the Alt (assuming it is Dr. Cheng).

If either the bomb, the incident alone, or both made the island sink, Dr. Cheng would have sunk with it. The only explanation is that the bomb didn't sink the island. Instead it nuetralized it's powers.

Without it's powers, there would be no reason for Cheng to hang around. He would soon leave the island to join his family. Perhaps at the same time that Ben and his father left. The Losties helped improve their relationships which explains some of the changes in the Alt. Ben's father was deeply affected by Ben getting shot. Likewise, Cheng got to meet his grownup son and did not want to miss seeing him grow up.

As for the island, I think without the pocket of energy it resided on, it gradually sank to the bottom of the ocean. Judging by the condition of the structures underwater, it did not happen quickly. It may have taken a few years.

I think some have similarly suggested that the bomb didn't sink the island, but I don't recall seeing it as a theory. Sorry, if I'm wrong about that.