H-bomb does nothing by Kimkim

OK so, this is a pretty simple theory I think, so I'm sure someone has already discussed it but if not here goes:

This relates to the whole time loop thing, which I think does exist. Just by going back in time they create a time loop where whatever happened in 1977 while they were in 2000-ish was in the past but now that they are in 1977 that is their present and 2000 is in the future. I also think this time loop is exactly what MIB was talking about when he said he was going to find a loop hole to kill Jacob. (I know other people have mentioned this but my theory builds off of this)...

My theory is that the h-bomb that Juliet detonated could not possibly have changed the past (making it so that the hatch was never built and the plane never crashes on the island). First of all I think that would make for a horrible twist but thats besides the point. My main reasoning for this is that if the h-bomb changed the past causing the plane to never land on the island then that would also change the fact that jack and everyone else ever needed to go back to 1977 in the first place. It would effect so many other events in the past that it would ultimately make it impossible for the h-bomb to have ever of been detonated in the first place. If the plane never landed on the island then Locke never would have told Richard to bury the h-bomb and Juliet would never have went into 1977 and detonate the h-bomb in the first place. SO essentially the h-bomb being detonated would just cancel itself out.. making it impossible to change the past to begin with.