One possible plot could be that Natsu is completely devastated by Lucy's death. He turns to alcohol as a way to numb the pain. His friends might try to reach out to him, but he pushes them away in his grief. He could start having flashbacks of their adventures together while drunk, which makes his pain even more intense.
His friends would be very concerned. Gray, for example, might try to physically stop Natsu from drinking more. Erza would likely be more gentle and try to talk to him, to make him understand that getting drunk won't bring Lucy back.
Often, there's a theme of self - discovery. Natsu might learn something new about himself when drunk, like hidden feelings or desires. Also, the theme of friendship is prominent as his friends support or scold him, which shows the bond between them. In some cases, the fanfiction might use his drunken state to explore a potential romance in a more unguarded way.
The guild would likely be in deep mourning. His friends like Lucy, Gray, and Erza would be devastated. They might initially go into a state of denial and then slowly start to come to terms with it. There could be a quest for revenge against whoever or whatever caused his death.
A fanfiction named 'Drunk Natsu's Night Out' could be a great read. It might show Natsu getting drunk at a local tavern in the magical world. His drunken state could lead to him getting into a friendly brawl or starting an impromptu party. The story could then focus on how his friends react and how they all end up having an unexpected and wild night together.
I think characters like Makarov, the guild master, would be there. He could give a really heartwarming speech about how he's seen Natsu and Lucy grow. Wendy and Carla would also be guests. Wendy might be helping with some of the decorations, using her magic in a creative way, and Carla would be there to keep Happy in line and also enjoy the celebration.
Maybe the story could start with Natsu and Lucy going on a special mission. During this mission, they face a great danger that makes them realize how much they mean to each other. Once they return, Natsu decides it's time to get married. The fanfiction could then focus on the wedding preparations, like Lucy choosing her dress and Natsu trying to find the perfect gift for her.
Natsu and Lucy don't tie the knot in the manga. The plot mainly centers around their friendships and the challenges they face together, not their marital status.
Well, in the manga, Lucy and Natsu do get married. Their journey is filled with ups and downs, but their love perseveres and culminates in a beautiful wedding.