Perhaps Snape is trapped in a dangerous magical trap set by Voldemort. Harry, having a connection to Voldemort's mind, is able to understand the mechanics of the trap. He uses his Patronus, which has grown stronger over the years, to break through the dark magic surrounding the trap. Then he enters the trap and pulls Snape out just before it collapses, saving Snape from certain death.
One possible plotline could be that Harry discovers a plot against Snape before it's too late. Maybe he overhears some Death Eaters planning to ambush Snape while he's on a solitary mission. Harry then uses his invisibility cloak and magic skills he's learned over the years to outwit the Death Eaters and save Snape. This would show Harry's growth as a wizard and his ability to set aside past differences with Snape.
In another scenario, Snape could be poisoned by a dark magic - made substance. Harry, with his knowledge of potions (thanks to Snape's strict teaching in the past), figures out the antidote. He races against time, facing various obstacles in the Hogwarts castle, like secret passageways being blocked and magical creatures getting in his way. But he finally manages to reach Snape and administer the antidote, saving his life.
Chapter 791, "There's Actually a Suona?!", is the clearest early answer because it turns Jiang Shixu's situation into a concrete plot event. The chapter turns that into something concrete by moving from The lights in the audience suddenly went out, and immediately, the...
Chapter 3 is the strongest chapter-level answer because it starts from Qiao was still annoyed at the attitude of this unknown girl when she heard... and follows through on Jiang Yan, forced into a marriage with someone he did not love, had....
Chapter 421, "Home Robbed", is the clearest early answer because it turns Home Robbed Mu's situation into a concrete plot event. It opens with Mu Ye was originally a fitness trainer. and closes on We've struck gold!" Nina immediately looked at the newcomers with....
Chapter 516, "Choosing You as an Undercover Agent is Pretty Stupid", is the clearest early answer because it turns Destiny's situation into a concrete plot event. The chapter turns that into something concrete by moving from Why are you skulking around and observing us?" Jiang Li cut straight...
Chapter 598, "She Blew Up Your Family's Lake!", is the clearest early answer because it turns Gu's situation into a concrete plot event.
Chapter 674, "Staring at Shu Yan", is the clearest early answer because it turns Aunt Li's situation into a concrete plot event. It opens with Wen Jiaojiao was about to say something else, but Jiang Li stopped... and closes on Although it was their first time dealing with Mr..
Chapter 657, "The Richest Man Becomes a Hardcore Fan?!", is the clearest early answer because it turns Crown Prince's situation into a concrete plot event.
Chapter 737, "Shu Yan in Trouble!", is the clearest early answer because it turns Bai Lu's situation into a concrete plot event.
Chapter 927, "Jiang Li: Deceased, Do Not Disturb", is the clearest early answer because it turns Zhao Lang's situation into a concrete plot event. Early on, Doomsday Beehive" made over fifty million in box office sales within.... By the end, Jiang Li kept desperately signaling Zhao Lang on stage..
Chapter 808, "Dare to Spank Him?!", is the clearest early answer because it turns Xiao Fan's situation into a concrete plot event.