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.
Their relationship in the fanfiction is likely to be full of mutual understanding. Since they are getting married, they must have a deep connection. Takato might be the more gentle and patient one, while Rika could be the strong - willed partner. They balance each other out.
The scene of Sukuna's death in the manga is a climactic moment. It's filled with action and drama, as various powers and tactics are employed to bring him down. The build-up to this point is full of tension.
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.