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.
Well, in an anime mashup novel, one key element is the blend of different anime universes. For example, characters from a shonen anime might interact with those from a magical girl anime. Another element is the plot which often has to be carefully crafted to make these different elements fit together. And the art style, even in written form, might be influenced by the distinct visual styles of the animes being mashed up.
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 novel approach could be using machine learning algorithms to analyze the context and requirements of the mashup project and recommend relevant APIs based on that.