There are some fanfictions that might explore such a scenario. However, it depends on different authors' creativity and the specific plotlines they develop. Some fanfic writers might be interested in exploring the relationship between Mara Jade and Luke Skywalker in such a context, but it's not a mainstream or canon storyline in the official Star Wars universe.
One possible plot could be them going into hiding to protect the unborn child from their enemies. Since they are both important figures in the Star Wars universe, there would be many who might want to harm the child for various reasons, like power or revenge.
Yes, there are quite a few. You can check out fanfiction.net or Archive of Our Own. Just search for 'Luke Mara Jade romance' and you'll find a variety of stories with different takes on their relationship.
One common theme is the power of love and how it can change and redeem. Their relationship often shows how two very different people can come together and grow. For example, in many fics, Luke's Jedi beliefs and Mara's more independent nature at first clash but then blend.
One of the common themes is definitely the exploration of the Force. Luke being a powerful Jedi and Mara Jade also having a strong connection to the Force, many fanfictions explore how they interact with the Force together. The theme of family also pops up. Even though they don't have a traditional family at first, they create a sense of family with each other. And of course, the theme of good vs. evil is there as they are often pitted against dark forces in the galaxy.
Sith cults could also be antagonists. They might sense the power of the unborn child in the Force and want to turn it to the dark side. They could launch attacks on Luke and Mara to either kidnap Mara or influence the unborn child through dark side magic or the Force.
One great fanfiction could be 'The Bond of Skywalker and Jade'. It delves deep into their relationship, exploring how their Force sensitivities interact. Another is 'Luke and Mara: A New Adventure' which takes them on a journey across the galaxy to face a new threat. There's also 'Mara Jade's Choice' that focuses on Mara's internal struggles regarding her feelings for Luke.
Some popular authors are 'JediWriter123'. Their stories often have a great balance between action and romance for Luke and Mara. Another one is 'StarWarsFanatic456' who is known for really delving into the characters' emotions. And 'GalaxyTalesAuthor' also writes some great fanfiction about them.
The characters themselves are very popular in the Star Wars fandom. Fans love to explore the romantic side of their relationships that wasn't fully explored in the official canon.
Character growth is another major element. Mara Jade might start off as a bit of a mystery, and through her interactions with Luke, she evolves. Luke, too, may change as he gets closer to Mara, learning new things about himself and the Force, as seen in some fan fictions where he discovers new aspects of the Force through her influence.