I just posted a comment saying something similar- but i dont think i've heard one good argument debunking the Whatever happened happened (WHH) theory- here's some facts:
1. Candles arm- injured in the incident, we see it injured AFTER the incident, suggesting WHH 2. Mrs Hawking sent Daniel back knowing he would die, because SHE KNEW she couldnt change it, no matter what (weak, i admit)
(minds gone blank now, i'm sure there are more things to suggest its true- just cant think of them now!)
However- this is the most important one:
3. As we've seen during season 5, Locke(ish), Ben, Sun, Lapidus, Ben are all in 2007. if oceanic 815 never crashed, events on island after Sept 22, 2004 would be VASTLY different and certainly wouldnt include anybody who was on oceanic 815
i heard some theory that the 1977 and 2007 timelines "co-exist" and that a significant event occurring in 1977 wouldnt change the future until "the corresponding day" in 2007. this is a massive load of bull-poo, and if it turns out to be true in lost i'll stop watching, events in 1977 must surely have an INSTANTANEOUS effect on the timeline and therefore if the swan was destroyted and 815 never crashed, the events in 2007 in s5 COULD NEVER HAPPEN. my theory is that the nuke was the incident and even if not, destiny will course correct and they will still crash and events will play out exactly as they did again in seasons 1-5. The only variance so far from WHH is the "uniquely special" desmond
here is a challenge to all of you to come up with a CONVINCING (bold and underlined) argument that WHH is not true, i'll look forward to reading it!