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.
It could be other elements from Japanese folklore. There are many supernatural beings and concepts in Japanese mythology that might have influenced his creation.
One common theme could be power combinations. Since Izuku has his own unique quirk in My Hero Academia and Sukuna is extremely powerful in Jujutsu Kaisen, fanfictions might explore how their powers interact or complement each other.
In the manga, Sukuna doesn't possess all 20 fingers. There are specific story arcs and events where his finger count changes based on the plot developments.