There are various pieces of media outside the game that foreshadow the events that come to pass.
The Book of Cain foreshadows some of the events that come to pass in the game,
And in the end of days, wisdom shall be lost
As justice falls upon the world of men.
Valor shall turn to wrath
And hope will be swallowed by despair.
Death at last shall spread its wings over all
As fate lies shattered forever.
Take note of Fate.
The Diablo novel The Order, hints at certain person and a diabolical curse.
In the Black Soulstone cinematic, take note of who Azmodan is speaking to... and what he is taking about...
You thought you were so clever, that you would outwit us all. One by one our brethren fell into your trap but not me. I defy you. I know the black soulstone is the key and it shall be mine. Soon my army shall pour forth from the shattered mountain ravaging this world and all hope of resistance . My minions "will" find the stone... wherever you choose to hide it. Then, at long last, Azmodan will reign as the prime evil.
If you have the Collector's Edition Blu-Ray/DVD there is some commentary about the possible fate of certain characters.
From "Leah's Journey," Chris Metzen: "Her spirit's still out there somewhere. There's a good girl there, that deserves to be saved and brought back from be abyss. So, while we don't have any clues yet what subsequent chapters will be (a couple of clues), I would bet that we would chase that down, because it feels right from the story level and it feels right from the character level."
There's still may question that are left unanswered.
The fate an Adria, the Black Soulstone (now that all seven evils are united...), is Leah's soul gone for good?