Sukuna does die in the manga. The way it happens is quite dramatic and ties in with many other elements of the story, adding depth and tension to the overall narrative.
No. Ryomen Sukuna is a fictional character from Japanese mythology and modern manga/anime. He doesn't have a basis in a true historical event or person.
Nope. Ryomen Sukuna has no basis in reality. It's a product of the creative minds of the writers and illustrators who designed a captivating fictional character for the enjoyment of the audience.
Character consistency. A good Percy Jackson headcanon fanfic keeps the characters true to their original personalities. For example, Percy should still be brave and a bit of a smart - aleck, and Annabeth should be intelligent and strategic. If the characters act out of character, it just doesn't feel like a Percy Jackson story.
A great Percy Jackson headcanon fanfic I recall is the one where all the demigods have a special mark on their body that represents their godly parentage in a more detailed way. For example, Percy had a trident - shaped mark on his back that glowed when he was near water. This added a really cool visual element to the story and also led to some interesting plot points, like when the demigods had to hide their marks from mortals or use them to prove their identity to other demigods.
One interesting concept could be alternate family relationships. For example, a headcanon where Percy has a long - lost sister who also has demigod powers. This could add new dynamics to his story and how he copes with family issues in the demigod world.