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.
One common theme is the power dynamic. Since Geto has strong powers in the Jujutsu Kaisen universe, exploring how that affects his relationship with the reader can be interesting. For example, he might protect the reader using his powers.
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.
One common theme is friendship. Their bond, whether it's growing stronger or falling apart, is often explored. For example, many fanfictions show how they supported each other in their early days as sorcerers.
One great fanfiction is 'The Bond Beyond'. It delves deep into the complex relationship between Gojo Satoru and Geto Suguru. It shows their early days at Jujutsu Tech, their training together, and how their ideologies start to diverge. The author does an excellent job of portraying their individual personalities and the strong connection they once had.
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.