The fate of the girl in the book. She's arrested as a witch to face torture and execution, despite, as Adso says, being the only true innocent in the whole affair. Adso can't do anything to help her, and he never even learns her name.
And even before that it's pretty brutal for her—regularly smuggled into the abbey to have sex with old and deformed monks, in exchange for food for her starving family. And the monks who do the smuggling in aren't even decent enough to give her something palatable—the packet she has with her contains offal, including a beef heart and pieces of lung.
The climax where the library burns down, the MacGuffin is destroyed and the murderer commits suicide rather than be brought to justice. Especially with Benno trying desperately to save his precious books.
What happened to Adelmo, whose death set the whole plot in motion—he finally consummates his relationship with fellow monk Berengar, and then overcome by guilt rushes to confess to Jorge who castigates him for the sin, likely refuses absolution, and drives him so mad with guilt that he ends up killing himself. It's a monk killing himself—Adelmo has been so browbeaten by Jorge that he considers himself already doomed to hell, so the sin of suicide won't make any additional torture.
Young Adso's loss of innocence as each ugly part of the plot is uncovered. He manages to hold onto his faith, but it's pretty brutal for the kid.
Years later, Adso returns to the now-abandoned site and gathers what fragments of books he can.
Salvatore insanely singing an Italian lullaby as he burns.
