This is a bit out there but I was trying to come up with other theories beyond the realm of a total reset or a time jump to 2007, which seem a bit too obvious for Lost. What if Jughead's detonation did change the past in a way, but yet Oceanic Flight 815 still crashed on the island on September 22 2004? I believe that it was ultimately Jacob's will that brought these people to the island on that fateful day. Desmond's failure to push the button was a mere coincidence. I believe that the detonation of the hydrogen bomb negated the need for the Swan to be built (if as Daniel was right the detonation negated the energy). Thus, the survivors would never have found the hatch in season one, paving the way for a different course of events to take place. I think Jacob's death is possibly a defining moment in the island's history, and I have a feeling that this different timeline will lead to the 1977 people either witnessing this pivotal moment, or doing something in its aftermath.
I believe Jacob brought Oceanic Flight 815 to the Island for a reason, not for their whole experience of Island life to be reset. Whatever happens this season, the survivors will find themselves on the Island, because it is fate's will and Jacob's will.
I guess we'll find out Tuesday, or Thursday for me in Ireland.