According to the Jenny Uglo bio of Elizabeth Gaskell(Elizabeth Gaskell: A Habit of Stories), Gaskell intended Cousin Phillis (Victorian Collection) to have a third part which she never wrote.
The story was serialized in the Cornhill magazine, and Gaskell and George Smith, the editor and publisher of Cornhill, had a misunderstanding regarding the amount of space he would give to her story. In a letter to Smith, Gaskell said that Cousin Phillis were she able to complete it as planned, had 'a sort of moral, "Tis better to have loved and lost, then never to have loved at all.'" Uglow goes on to recount the sketch of the ending, saying that Gaskell planned that the "last scenes would be set years later, after Holman [Phillis's father] had died. Paul, now married, returns to find Heathbridge struck by typhus and comes across Phillis using Holdsworth's old technical sketches to help her drain the marshy land. An independent single woman, working in harmony with the 'common labourers', she uintes male knowledge with female love: Paul finds her with an orpphaned child in her arms, and 'another pulling at her gown'--we hear afterwards that she has adopted them."
I love this ending. Much as I liked Betty telling Phillis to get up and live, we don't see Phillis moving on from Holdsworth, and so the part that is finished does feel truncated, abrupt in its closing.
This unwritten sketch provides a much more complete and powerful picture of Phillis. So why didn't Gaskell write the ending anyway? With other serialized works, notably North and South (Oxford World's Classics), even though she was rushed at the end, she did go back and rework them to some degree, though I'm not sure ever to her satisfaction. After the Cornhill serialization, she could have written her ending as she wanted it. I find it curious that she didn't, but then, in reading her bio, it seems that she truly did try to do too much. You almost feel the mania that drove her from project to project, managing her family, her stories, her life, until she finally collapsed at the young age of fifty-five.