I believe more that it's multiple realities than timelines. There are an infinite number of parralel universes in which every eventuality is played out. So maybe in a certain parralel world "Go and get my dad and if I'm drunker than him" Jacks dad wasnt in a coffin on the plane when it crashed, Jack managed to meet him before he died in Australia and they were reconciled. Charlie " I'm dead but I'm also here" Dead in some worlds but not this, maybe he's found out how to jump between the worlds (as I believe Ben may have). In another parralel world, Aaron really is Kates son - it was really Kate who was pregnant when her version of 815 crashed and it was Claire being taken back to face justice. This can explain more or less everything in the show (which is why I like to think that this is whats going on, as I'm very confused lol).

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Go then, there are other worlds than this.