You can find an entire translation of all the remaining areas on Appinvasion(took me a while to find it myself the first time). This is a rough summary of what I myself read yesterday, so if I made some errors, note you can check the facts yourself in the translations.

Summary of the story (as well as what will be coming after you defeat Lucious and why)

This is partial summary of what happens in the final area after the Eriole part described in this thread by Rakhinos.

1)You progress into the final area encounter the Masked figure who's name is Arc. -You learn he was a powerful figure known as the Knight of Revelation and was responsible for killing (some) of the original 6 heroes (why further down) -You end up initially fighting Tilith in the fire area, who has been commanded by Lucious to destroy you if you keep pushing forward. She clearly indicates she doesnt want to -Fighting Tilith you guard each turn for 5 turns and she pleads why you aren't attacking and ends up surrendering herself

2) Arc (The dark figure) appears here and as you progress through the areas. He explains he too is a servant of Lucious then reveals he wants to humanity survive and ends up helping you and Tilith as he reveals the history of Lucious, Karna Masta, and what problem will occur once Lucious is defeated (below).

3) Arc explains Karna Masta is the one who issued the order to wipe out humanity and that Lucious saw it would *not** be good** for the world to do so. He planned with Arc as well as a powerful shrine maiden to combat Karna Masta after he is weakened by Lucious. Arc combats Karna masta, and Lucious proceeds to seal him once hes weak enough, but also seals off the Shrine maiden who is Arc's lover as hostage. This is why Arc has to obey Lucious and kill the six heroes.

4) Arc also reveals that once Karna Masta was being sealed Karna Masta made a last curse which was granting humans the power to summon as a means to defeat Lucious. This is why Lucious then came to fear humans with this power

5)Arc reveals that when Lucious is defeated a gate he seals to the Demon world Ishgalia will fall and this will allow powerful demons to come through. He reveals that a small crack allowed weak demons to come through and that Graham is only a weak demon, nevermind whatever higher demons exist in Ishgalia.

6)When Lucious is defeated, the plan is for Tilith to absorb Lucious remaining power to attempt to keep Ishgalia sealed. This requires her to also bascially be a prisoner in order to do so (check this). Arc would combat demons during at this gate, while Grahdens advises you all to return to the summoners hall and communicate the "danger coming next" being the Demons of Ishgalia.

To summarize: Tilith is left holding off whats left of the seal, Karna Masta is still hidden/sealed so he will obviously become an opponent later, and the demon world will be explored.

Hope that is what you are looking for as in what happens after Afla Dilith.