Alecto dies in a hospital room in St. Mungo's two days after the battle.
There was some debate over taking her there. Some want to leave her to bleed out. Neville Longbottom champions her cause, urges the others to get her medical care.
In the end they decide to be the better people and scrape her off the Ravenclaw common room floor and ferry what's left of her to the hospital.
They needn't have bothered really. Alecto's injuries are too great-who ever attacked the Carrows backed up their beating with curses that make healing her wounds almost impossible. She never stirs in her hospital bed.
In the end, the gesture of mercy given by the heroes of Hogwarts to Alecto Carrow is futile. She dies anyway.