Margot I guess that's true about Oregon/Melissa from Fresh Meat and Barbara from Call the Midwife being not that different. I am sure Barbara would never have dreamt of sleeping with her married lecturer though!
And Scrabbler I love the idea of Oregon being Barbara and Tom's granddaughter, as you say the family background and the timeline could be right. But Barbara and Tom never got the chance to start a family. 
However, if I am not satisfied with a plot ending, I decide it's the way I want in my head. For instance Carl's death in 'The Walking Dead' - never happened. Joe dies at the end of 'Medium' - nope. The Desperate Housewives all moved away from each other and never met again - no, not in my world! So in my head Barbara and Tom have moved away to the country and Barbara is now pregnant with Oregon's Mum/Dad.
Don't know what would happen to the Tom character without her though, like pps said, I can't see him getting back with Trixie, they are too different. (Even though the actors are together in real life, of course).