Nathaniel Hawthorne's classic novel The Scarlet Letter might be considered an open-ended novel if you mean the ending has several unanswered questions. How the novel ends for Hester is fairly straightforward. She and Pearl left America and went to England where Pearl presumably grew into a fine young woman who married nobility (remember she was extremely wealthy because of Roger Chillingworth). By the hints we're given, we surmise that Pearl moved to a foreign country, had at least one child, and treated her mother well despite the distance between them. Hester eventually simply died in the house where she lived out most of her shame, and she loved Arthur Dimmesdale until she was finally buried next to him.
The end of Arthur's story is a bit more ambiguous. We know he had a renewed sense of energy and life after his meeting with Hester in the forest, and that energy sustained him through his Election Day Sermon. Once he finished, something happened to him. We don't know what his sermon was about, but we know he had barely enough energy to walk as far as the scaffold. Once there, he made a sort of public confession which was open to interpretation by those in attendance. What changed, what the crowd did or did not see, what caused such a change of heart, what he spoke about in his sermon--all of these unanswered questions create a sense of ambiguity which can be read as open-ended.
thank u so much for the beautiful answer :)