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.
As of the latest chapters I've read, Megumi is still alive in the manga. Usually, such major character deaths are significant plot points and would be well-publicized if they occurred.
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.