She might survive by making use of her relationships. For instance, if she has some sort of connection with Loki (maybe from past encounters), she could call out to him telepathically (if there's some sort of magic involved). Loki, being the trickster he is, could then come and rescue her. Another way is that Darcy could use her knowledge of science to create a makeshift weapon or a device that would help her escape from Hydra's clutches. She could use the materials available in her cell to build something useful.
A possible plot for a 'Hydra Kidnaps Darcy' fanfiction could involve Darcy's sassy attitude getting on the nerves of her Hydra captors. This could lead to some humorous exchanges while still maintaining the tension of the situation. Meanwhile, the Avengers are frantically searching for her. Captain America might use his leadership skills to coordinate the search efforts. Back with Darcy, she could try to form an alliance with other captives in the Hydra base. Together, they could come up with a plan to revolt against their captors and escape before the Avengers arrive.
One possible outcome in this fanfiction could be that Loki kidnaps Darcy for a very specific reason. Maybe he needs her knowledge of some scientific concept that is relevant in the world he is from or is planning to use in his schemes. For example, if Darcy has been working on some sort of energy research that Loki believes can be harnessed for his own power - enhancing purposes.
Well, I'm not sure of specific 'Winter Soldier kidnaps Darcy' fanfiction titles off the top of my head. But you can also try FanFiction.net. Sometimes fan communities on social media platforms like Tumblr might also discuss or recommend such stories. They could be a good source to find what you're looking for.
Perhaps the kidnapping is part of a larger plot by an enemy of both the Winter Soldier and Darcy's friends. The Winter Soldier might be used as a tool, and Darcy could end up being the key to breaking his brainwashing. She could start to form an unexpected connection with him during her captivity, leading to a change in both of their fates.
Loe might also be able to save himself depending on his own character traits. If he's really smart, he could outwit Darcy and escape on his own. But considering he's been kidnapped, it's more likely that he'll need some outside help, and the Avengers are the obvious choice given their reputation for protecting the world in these kinds of fictional stories.
In some Harry Potter fanfictions, 'hydra' could be a magical experiment gone wrong. A wizard or witch might have been trying to create a new form of life or a powerful spell, and instead, they ended up with something similar to a hydra. It could also be a name given to a place, like a hidden lair or a dangerous area filled with all sorts of magical perils that the characters need to navigate through.
It could be a powerful antagonist. The three heads mean it has multiple ways to attack and defend. It might be very difficult for the heroes in the fanfiction to deal with.
In TF (Transformers, I assume) fanfiction, a 3 - Headed Hydra can be a really interesting and unique addition. It could represent a powerful and menacing force. Maybe it's a new kind of enemy created by a Decepticon scientist. It might have different abilities in each head, like one head spits fire, another head has a freezing breath, and the third head can emit a sonic blast to disrupt Autobot communications.
In 'Percy is a Hydra' fanfiction, one characteristic could be a change in Percy's physical form. He might have some Hydra - like features, such as multiple heads or a scaly body. Story - wise, there could be a struggle between his original self and the new Hydra - influenced self. The plot might revolve around how he copes with this transformation, how his friends and enemies react to it, and how he uses or overcomes his new Hydra - related abilities. It could also explore themes of identity, acceptance, and the blurring of the line between hero and monster. This type of fanfiction often takes the original character of Percy and subverts the reader's expectations, creating a whole new and often very interesting narrative.