There are numerous books out there, and without more details about this 'Sam Hell Book', it's difficult to say for sure if it's a true story. It could be a fictional work with a character named Sam Hell, or it could be based on real events but highly fictionalized. Some books claim to be 'true stories' but may contain elements of exaggeration or misinformation.
The book is not a true story. It's a creation of the author's mind, using elements of fiction to build an engaging narrative that may or may not resemble real life in any way.
In fanfiction, if Sam was kidnapped, it could lead to a very intense story. Dean would surely go on a rampage to find him. Maybe Sam was kidnapped by a powerful demon who wants to use him for some dark ritual. It could also be a new, unknown enemy who has a vendetta against the Winchesters.
Obviously, Sam Hell is an important character as the story is about his extraordinary life. There might be his family members like his parents, who could have a great influence on his upbringing and the way he views the world.
Dean is almost always going to be in these fanfictions when Sam is gagged. Their relationship is central to Supernatural. Rowena could also be a character. She might use her magic to either gag Sam for her own purposes or to help him if she has a change of heart. And Gabriel. He could turn up and use his trickster abilities to either put Sam in the gagged situation as a joke or to get him out of a more serious one.
In fanfiction, Dean as a Prince of Hell can open up many interesting storylines. One possibility is that his character becomes darker and more conflicted. He might struggle with his newfound powers and the evil that comes with being a Prince of Hell. His relationships with Sam and Castiel would also be severely tested as they try to figure out how to deal with this new Dean.
In many fanfictions, Dean as a Knight of Hell can bring a whole new dynamic to the Supernatural universe. His relationships with other characters, like Sam, would be severely tested. He could be seen as a threat by some and a potential ally by others who hope to control or redeem him.
One great fanfiction is 'Sam and Rowena's Unlikely Alliance'. In this story, they team up to face a powerful new threat that the Winchesters alone can't handle. It has a lot of great character development for both Sam and Rowena, showing their complex relationship in a new light. The author does a wonderful job of capturing their voices, making it feel like an extension of the show.