Well, if we're following the common ships in the Fairy Tail fandom, Natsu could be a likely candidate. Their relationship is very close and there are many hints of a deeper connection between them in the original series. It would make for an interesting story as Natsu would have to grow up a bit to take on the role of a father.
Gray could also be a possibility. He and Lucy have a friendly rivalry and there are moments where their relationship could be interpreted as having deeper feelings. It would be an interesting twist if Gray was the father, as it would change the dynamics between him, Natsu, and Lucy in the fanfic.
Some writers justify Lucy's death by making it a noble sacrifice. For example, she might give up her life to close a portal that would otherwise release a great evil upon the world. This way, her death is seen as necessary for the greater good of the entire Fairy Tail universe, including all the kingdoms and innocent people in it.
If Lucy never joined Fairy Tail, the friendships and relationships among the characters would form in a very different way. Also, many of the story arcs might not unfold as they do in the original plot.
In some fanfictions of Lucy's death in Fairy Tail, a heartbreaking scene could be when her friends find out she sacrificed herself to save the guild. They might come across her lifeless body surrounded by the remnants of the great battle she fought. It's a moment of shock and extreme grief for them, realizing they've lost such an important member.
When Lucy dies in a fanfiction, it might cause a rift among the guild members. Some may blame themselves for not being able to protect her. Her death could also be the start of a new adventure as the characters search for a way to resurrect her. This could lead them to explore new magical realms or encounter new enemies. Plus, it could change the power balance in the guild as her celestial magic was quite unique and important.
Happy, Natsu's companion, would also be very sad. He was used to Lucy being around and would miss her presence. The whole Fairy Tail guild would be in mourning. Erza, for instance, would feel a great sense of loss as Lucy was like a little sister to her. This could lead to changes in the guild's dynamics, with some members becoming more withdrawn while others might try to be stronger to honor Lucy's memory.
One popular theme is Lucy's growth as a wizard. Fans often explore how she overcomes new challenges and becomes stronger. Another theme is her relationships, not just romantic ones but also her friendships within the guild. For example, her bond with Natsu and how they support each other through tough times.
One possible scenario could be that she sacrifices herself to save her friends from a powerful dark magic. In the chaos of a huge battle, she might use all her magic power to create a shield that protects everyone else but drains her life force completely.
Well, to find a Fairy Tail fanfiction involving Lucy and Froch, start with checking out dedicated Fairy Tail fan communities. These communities often have their own sections for fanfiction. Maybe post a request there asking if anyone knows of such a fic with Lucy and Froch. Another option is to use Google. Type in something like 'Lucy Froch Fairy Tail fanfiction' and look through the search results. Some of the top results might be what you're looking for.