Here's how I think that this movie should be if there was a sequal
So Colin's dad was deeply depressed after the death of his wife. But at the end, he came out of it. So here's how I think it should end up. Mary and Dickon get married when they are older, because you could tell that they had something for each other. Now after Lord Craven comes out of his depression, he starts looking for a wife. He notices that Martha, Dickon's sister, is quite nice. Yeah, she's young, but hey, age differences weren't all that uncommon back then and still aren't. So to make a long story short, Lord Craven and Martha end up getting married and a year later, they give birth to a baby girl.
This will continue, but I gotta go some homework.