I've read that the ringworld's design is actually unstable, and that it would drift and eventually collide with the star it was supposed to orbit. How is this flaw corrected in the subsequent stories?
Niven didn't have any intention of writing a sequel, but this big flaw in the Ringworld led him to write The Ringworld Engineers. In that novel, the ring has several attitude jets that are powered by the solar wind.
The plot revolves around the characters attempting to locate the control and repair center of the Ringworld in order to replace some of the broken and stolen attitude jets.
Teela Brown, now a protector stage human, realizes that it is too late to stop the drift by simply fixing the attitude jets. The only solution she envisions requires using the Meteor Defense System, a supercondutor grid that lies below the Ringworld's surface and can generate powerful magnetic fields, to induce an enormous solar flare. Such a flare would provide enough power to rectify the Ringworld's orbit, but would kill trillions of Ringworld inhabitants. Unable to live with that choice because of her protector instincts, she engenders a plan for Louis Wu and his crew to kill her and then put the plan into motion.
The Ringworld is outfitted with engines that stabilize the ring against wobble and from falling into the sun, they harvest solar wind for power.