I have heard many times that the H-Bomb is not the reason the Island sunk, they say because "Ben is still alive and out of the Island on Locke's Flash Sideways". Well it may be that the H-Bomb didn't sink the Island, and while that may be true I can show you how it is possible the Island sank because of the H-Bomb. When Juliet made Jughead explode there was the possible paradox, if 815 never crashes then who goes back in time and create the events that set off the explosion of Jughead. Because of this paradox the timeline splits and we get the two realities we are watching right now, and Oh Boy Ben is not an evil SOB and he's off the Island. Well this is because Ben was never shot by Sayid, I know that the timeline split when Jughead detonated and everything before that event was the same, except for what our time travelers did because in this timeline they never came to the past. The timeline just diverged, it is a Paradox, and I may be wrong about this but I just think that saying that because Ben is out off the Island the H-Bomb didn't sink the Island isn't necessarily a confirmation of this. Also worth noting that we only saw one scene of the guy, we can't say that he is not evil. Or that he is evil because he was saved by the Others, he may have changed through a long period of time, maybe because he wasn't on the Island for a long period of time after he was cured these personality changes weren't as dramatic as they are in the other timeline. Also also worth noting, we do not know the effects the H-Bomb had and how if it did sink the Island. I personally believe that the H-Bomb caused the sinking of the Island through a chain reaction of effects that started when the bomb exploded, it may have also been through a not so short period of time.