What will Snape do now that he's no longer in love with Lilly?
Nothing. They are no longer counting on him to protect Harry from a returned Voldemort. Unless you mean whether he is going to evolve as a person and maybe develop a love life.
How was magical Italy ruined 323 years ago, or does it matter?
I suspect it was only an example of how yes, Potterverse magic can be that destructive (something we would not guess based on canon).
Quirrell teaching students the Killing curse...will it matter?
Unlikely. Knowing the Killing Curse is perfectly legal, and a lot of people have managed to learn it even though it is not taught in school. Come to that, the information we have suggests that it is also perfectly legal to use, just not against humans (unless they are Death Eaters, assuming the Monroe Act hasn't been repealed).
Why did the rememberal go off?
Because Harry has a lifetime's worth of lost/repressed Tom Riddle memories. We know that they're still in there somewhere, because he recovers the memory of his imprinting and of the locations of Voldemort's five "elemental" horcruxes.
This is a new thread to discuss Eliezer Yudkowsky’s Harry Potter and the Methods of Rationality and anything related to it. This thread is intended for discussing chapter 116.
There is a site dedicated to the story at hpmor.com, which is now the place to go to find the authors notes and all sorts of other goodies. AdeleneDawner has kept an archive of Author’s Notes. (This goes up to the notes for chapter 76, and is now not updating. The authors notes from chapter 77 onwards are on hpmor.com.)