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.
Gomi Gojo's Territory Opening Gesture was an important element in the " Return of Curse ". Gotto Gojo's domain was displayed as 'Boundless Empty'. This gesture was to pull the enemy into the infinite inner side, forcing the enemy's brain to produce a large amount of information, causing the brain to lose its function and could only stand and wait for death. Although there was no specific description of the hand gesture, it could be speculated that the hand gesture was to expand the domain through a specific posture of the hands.
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.
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.