Reading all of these theories day after day, i find it incredibly shocking that the very little overall analyses mention Faraday playing into it. Here's a short list of what i believe to be groundbreaking known facts about this character that can only mean he is returning in a big way to Lost.
- He was killed before he was born. His life ended before it began. I find this to be incredibly significant because he is the only main character to my recollection that this is true for. A few random survivors were killed off in the arrow attack of "the lie" which took place in 1954 so obviously a few of them this is true for as well, but as far as living and somewhat important characters go, Faraday is the only one.
- His illness. I believe that he tried to send himself to the future, to the island during the time of the finale events in some way (possibly through interacting with Eloise - how long has she been the caretaker for The Lamp Post?), even if only for a short period of time. Faraday has yet to pull off something incredible.
- If somehow the alternate timeline were to merge, Daniel could come back to life (its a somewhat far-fetched theory but this is lost after all) in some way. His body wasn't buried on-screen ever so who knows what Eloise and/or Richard did with it.
- Faraday was an incredibly well-liked character and the writers/producers must know this. I seem to recall there being somewhat of an uproar when he was killed off so abruptly after returning. This could be just a big fake-out the writers of Lost are famous for.
-He had very significant interactions with a few of the most important characters of the endgame of Lost:
---Desmond, who is clearly going to be the most interesting and mindblowing to watch in the finale. Desmond proved to Faraday that his experiments have real potential and real purpose which could have lead to his illness. Desmond's love interest is Penny as we know - Penny is related to Faraday.
---Jack. THE character of Lost. He carried on Daniel's plans to detonate Jughead, which had monumental consequences that we still don't know the real extent of yet.
---His parents. Charles Widmore and Eloise Hawking. 2 characters that are alive and well and i fully expect to see in the finale.