Firestorm
I think the flash sideways universe is in fact the epilogue. The characters that appear in them are the ones who did not become the new Jacob, and thus will have their lives return to normal (not necessarily good). IMO, we should be keeping our eyes open for characters that DONT appear in the flash sideways, as they are the most likely successful candidates.
A: The flash sideways could be an epilogue but, perhaps, it could be a sideways prequel leading the Losties to the island. The only person that we know of so far that has any indication of the island is Ben and Roger. Ben could take Roger back to the island as a last request due to his health. Roger just may want to live his last years sitting on a beach, earning 20%.
B: There is no new Jacob (yet). Jack is the most likely candidate (no pun intended), according to recent polls, which showed Jack on top of, well no one, as long as he was on the island, Sawyer got all the poon (Kate, Ana Lucia, and Juliet), and, well maybe Jack got some
Friendly strange. My Vote goes to Hurley for either the next "Jacob" or "Richard Alpert", which means being the advisor to whomever becomes "Jacob". I only say that b/c Richard is ready to retire and leave the island where he'll live the rest of his days in a valley surrounded by mountains.
C: Each of the next episodes are all character centric. For example the last episode was Bencentric. I know we have Richard, Sun and Jin, Hurley, and Sawyer centric episodes coming. The entire list of who the centric is, is TBA. So, just because they haven't been shown yet doesn't mean that any missing character will not play a pivotal role. C. Widmore is about to show up which will probably lead to (hopefully) Eloise Hawking, Daniel Faraday, Charlotte Lewis, and brother Desmond also appearing. So only time will tell...
*Since Ben left the island possibly before the incident, that would initially mean that C. Widmore was still the leader of the people. We can only assume that he left the island as before and fathered Penny. Or maybe not. He already has a baby mama on the island but, maybe he freaks out after she freaks out because she killed there son from the future. There is still the unknown reason as to why he was leaving the island originally. Isn't Penny older than Daniel anyway?