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, 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.
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.
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.
One great fanfiction could be where Dean and Sam have to face a unique Halloween - themed monster. Maybe a witch who uses Halloween traditions to cast powerful spells. They would have to use their wits and hunting skills to stop her before she causes chaos in a small town.
There's this fanfiction called 'Sam and Jack: Unlikely Allies'. It starts with them being at odds with each other, but as the story progresses, they start to understand and respect one another more. The plot is well - paced, and the author does a great job of writing their dialogue in a way that feels natural to their characters.