I like the theory, but the only fly in that ointment is the idea that was first brought up by Charlie, then further explained by Daniel. The idea that in the alt timeline, they are not "supposed" to be there. It's not what their lives were meant to be.
Ugh, I had forgotten that line. Do you suppose it could maybe only be referring to Charlie and Daniel? Maybe
they're "supposed" to be died in either timeline, but it doesn't refer to Sayid, Jin, Sun, etc. At this point, I could deal with that. I love Charlie, but I've already gone through my seven steps or whatever it is and resigned myself to the fact that he's gone. And Daniel, well, I feel kinda sorry for him, but that's about it.