In Act 3, the mission is to trap all of evil lords in the black soulstone, and then shatter it. Leah is a pretty significant part of this, as her powers are what allow us to transfer the demonic souls into the stone. Throughout the campaign story, Leah is a vital and integral role in the plot development.
However, there's this huge shift in perspective once Adria betrays the Nephalum, and shoves the soulstone into Leah's forehead. With the evils congregated, they're stronger than ever before, and Diablo is going to wreck everything. Diablo is running amuck in The High Heavens, and only the Nephalum can stop him, because he's debilitated all of the angels.
There was one thing Diablo didn't consider about this plan:
What happens if he's defeated?
With all of the evils contained in a single stone, it is MUCH more difficult for them to find a new host. There are no siblings to bring Diablo to fruition again. In short, Diablo is gone for awhile, if not forever.
Now here is where the issue lies.
In the cut scene, Tyrael is yabbering about the Nephalum, and how great he is, and that humanity is dawning blah blah blah, and that he is reclaiming his place as a mortal angel. Diablo is shown falling from heaven, disintegrating, with the black soulstone falling and no sign of Leah. And still, Tyrael is going on about Nephalum this, Nephalum that, and there is ABSOLUTE NO MENTION OF LEAH'S SACRIFICE OR EVEN HER EXISTENCE.
Leah was a GREAT character. I attached to her not only because of Deckard Cain, but also because she is the freaking protagonist of the story, aside from the nameless Nephalum who is so great and kick-!@#. She's featured in every cut-scene, yet there is no mention of her name in the final scene.
I just don't get it. Why? She deserved at least a somber rememberance, or some crap.