What happens to jacky in the book after Leonard dies? I don't think the author says. In real life what would have happened to her, I wonder? But the failure to tell us may demonstrate the author's attitude to her - she is not really important, what he cares about is the resolution of the middle class predicament, not the plight of the poor.
Interesting point a pp made about the danger Helen was in - I had not appreciated that at the time I read the book. Margaret stepped up then it is true. But once you start asking yourself why Helen returned to Howard's End, there's no very good reason plot wise. I can see that she came back to England to see Aunt Juley, but really if she was in such a terrible social situation would she have gone to HE to pick up a few books?