Well, Cid Kagenou does reveal himself at a crucial point in the manga. This reveal has significant implications for the plot and character development.
I don't have a definite answer for you. The manga might be keeping us in suspense about who Cid Kagenou will end up with. It could be a surprise twist or a character that has been hinted at throughout the series.
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.