'You're good Jackie' - last scene - spoilers -
If you go back and watch Season 1, episode 1, Jackie quotes a Saint (Augustine?) As he prayed to God. "Please make me good God, but not yet." This is Jackie all the way.
She could not ever give up her vices.
And she had this great capacity to be good and just as great of capacity to be evil, as she mentioned her 10th grade nun spoke of...
As she is lying there clearly dying in the series finale, Zoey is saying "you're good Jackie" This is Jackie's release. She can be good for God now, since she is done with her earthly vices. In my opinion, Jackie most certainly dies.
And just common sense (plus Pulp Fiction) tells us that much less heroin than what Jackie took down would make someone OD.
This was her suicide. This is her most despicable move yet... she committed suicide because everyone was leaving her. But Fiona was expecting her at the confirmation, so my heart breaks.