At what point did Alice's book/screenplay finish? (Spoiler)

Was it when David fell over the bannister or was it when her friend Rebecca found her in the bath and put on the bed. Could the the ending of the movie actually be the ending of her book and Alice was in reality still alive, perhaps downstairs preparing her manuscript for the publishers. Everybody seems to thing that the bit where her friend finds her in the bath etc was not part of her novel, but I wonder.