.. Hmm .. I'm just thinking that in Flash before your eyes the ring lady says something like desmond will be in the hatch for 3 years until he is forced to push the fail safe key, if you don't do that every single person is dead. So on the last epi on season 2 when desmond sees the papers seeing that he crashed the plane desmons says ''you'll kill us all'' and! i don't have to say anymore just check out the link about what happened then > YouTube - System failure
some how I tink lock was right when he said ''I've just saved us all'' and I tink he did save em. Maybe the same with Entering 77 after all it said enter 77 if a hostile has taken over .. and he did , so it wouldn't just blow up for no reason. I think since Locke entered the numbers .. it's saved them somehow again , maybe we'll found out later, but it's what I think anyway.