If Merlin died in the fanfiction, it could trigger a series of tragic events. The balance of power could tip, and the villains might seize the opportunity to attack. It could also bring out hidden strengths in the remaining characters as they try to cope with the loss.
In a more humorous take on the 'Merlin tied to a bed' fanfiction, it could be that Merlin has fallen ill and the overly - protective Gaius has tied him to the bed to make sure he rests. Merlin, being the active person he is, complains constantly. Arthur comes to visit and teases Merlin about finally being still for once. Meanwhile, Merlin tries to convince Arthur to let him loose, promising that he'll be fine. Eventually, Gaius relents and unties Merlin, who then immediately starts bustling around the room.
It could be for comedic effect to lighten the mood and add some fun to the story.
If Merlin is a Dark Lord in fanfiction, it could be an interesting exploration of the 'nature vs. nurture' concept. Maybe he turned dark because of the constant fear of being discovered and persecuted for his magic. His actions as a Dark Lord might include taking over Camelot or exacting revenge on those who wronged him in the past. It gives a whole new perspective on his character.
One more idea is that Merlin is tied to the bed in a dream - like state created by an ancient magic. In this dream world, he is faced with his deepest fears and insecurities. His friends in the real world notice his strange behavior and try to wake him up. Merlin, while in the dream, has to find the source of the magic that is binding him and break free. Through his inner strength and the memories of his friends, he manages to do so and wakes up, having learned more about himself and his magic.
One possible reason could be a magical curse. In many Merlin fanfictions, magic is often used as a plot device. A dark sorcerer might cast a spell on Merlin to make him forget certain things, perhaps to prevent him from using his powerful magic to oppose them. Another reason could be a self - imposed forgetting due to trauma. Merlin has witnessed and endured a great deal of pain and suffering. To protect his own mental state, his mind might subconsciously block out certain memories.
Perhaps some of the snooty nobles who look down on Merlin and constantly try to get him into trouble. They could be making fun of his clumsy ways one too many times and he just snaps and hits them with a shoe. It would be a moment of satisfaction for the readers who don't like those arrogant characters.
Little Tian was resurrected after Merlin died. Tushan Jing used his body to protect Xiaoyao's body. Xiang Liu risked his injuries to take away Xiaoyao's body. Xiang Liu sacrificed a lot to save Xiaoyao. He sacrificed two of his own lives and fed Xiaoyao with his heart blood every day for thirty-seven years before Xiaoyao was revived. Later on, Xiang Liu taught Xiaoyao archery so that she could protect herself. Had he not watched enough of Long Lovesickness 2? Hurry up and read the original work of " Everlasting Lovesickness 2: A Vow of Love "!
He could become a Dark Lord due to betrayal. If someone he trusted deeply, like Arthur perhaps, turned on him because of his magic, it might push him over the edge.
Some might be shocked. For instance, Morgana, who has her own complex story arc, may be taken aback by how fans rewrite her motives in fanfiction. She might not expect certain sympathetic portrayals.
Arthur could visit Merlin in the tower. He might be curious about what Merlin does in his secret place or he could be in need of Merlin's help and follows him there.