Another ending could be that Sarah and Jareth reach a compromise. Jareth lets her go, but she promises to visit his world from time to time. This ending allows for a bit of a bittersweet separation while also leaving the door open for future interactions between the two characters.
The story might end with Sarah actually falling in love with Jareth. She decides to stay in his world and they rule the Goblin Kingdom together, bringing a new era of peace and harmony between the human world and the Goblin realm. This would be a very different ending from the more common 'escape and return home' trope.
One interesting plot could be that Sarah, after being kidnapped, discovers a hidden side of Jareth's kingdom that he has kept secret from everyone. She finds out that there are other captives there who are being held against their will for reasons she has to uncover. As she tries to escape and free the others, she starts to see Jareth in a different light, not just as a captor but as a complex being with his own motives and past traumas.
The relationship might become more intense. With the pregnancy, they have to rely on each other more. Jareth may show his softer side as he takes care of Sarah, and Sarah might start to see him in a new light, beyond the intimidating Goblin King.
A common theme is the exploration of their unspoken connection. Since in the original there's a certain tension between them, fanfictions often expand on that, like in 'The Unspoken Bond' where it's all about their unacknowledged feelings for each other.
Perhaps they are forced to take care of a magical creature together. This creature could be a key to saving the Labyrinth. As they raise it, they learn about each other's parenting styles. Jareth, being used to ruling with an iron fist, has to adjust to Sarah's more nurturing approach. This experience makes them respect and care for each other more, and also gives them a common goal that deepens their relationship.
One great Jareth and Sarah fanfiction is 'The Labyrinth's Echo'. It beautifully explores their relationship post - the events of the Labyrinth. The author really captures the essence of Jareth's allure and Sarah's growth.
You can start by looking on Archive of Our Own (AO3). It has a large collection of fanfiction for various fandoms, including ones about Sarah and Jareth's love.
In a fanfiction about their reunion, the development of their relationship might be slow and gradual. Jareth, being a complex character, might not be able to easily let go of his old ways of being controlling. Sarah, having grown up, would not tolerate that easily. So they would have to find a common ground. As they interact more, they might find that they have more in common than they thought. For example, they both have a connection to the Labyrinth. This shared connection could be the starting point for them to understand each other better. Over time, this understanding could lead to a deeper relationship, whether it be a friendship or a romantic relationship.
Love in this fanfiction could be shown as a force that gives them the strength to face the unknown. The pregnancy is full of uncertainties, like what the baby will be like, how they will raise it between two worlds. But their love for each other and the baby gives them the courage to face all these questions. They support each other emotionally, and their love becomes the foundation for building a family, despite all the odds against them.
Well, Sarah's character could be developed in a way that she has to balance her normal life outside the Labyrinth with her new role as a mother in the Labyrinth world. This would add more depth to her character as she tries to integrate two very different aspects of her life. Jareth, having a baby with Sarah, would have to reevaluate his power and his place in the Labyrinth. He might start to see the Labyrinth not just as his domain to rule but also as a place to create a home for his family. This would transform his character from a self - centered Goblin King to a more family - oriented one.
One common theme is the power dynamic between them. Since Jareth is a powerful Goblin King and Sarah is a mortal girl, exploring how their relationship develops in terms of power is popular.