I am inclined to believe that he wasn't defeated - the body everyone believes to be his had been "burnt to a crisp", which is inconsistent with everything we know about the Killing Curse.
Assuming, however, that the official account is accurate, the logical next step would be to learn the True Patronus Charm, the only thing he knows which can block a Killing Curse. He might also want to study Harry for lingering magical effects (if any such effect can endure over twelve years), though this is made more difficult by the resonance effect.
Do we know the True Patronus blocks the Killing Curse ? My own interpretation was more than Quirell-Harry magical interaction made both spells to fizzle when they interact (like in canon, where repeatedly Voldemort casting AK on Harry leads to unexpected results), but it wouldn't work with someone else casting either of the spells.
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 chapters 91 & 92 . The previous thread has passed 500 comments.
There is now 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.)
The first 5 discussion threads are on the main page under the harry_potter tag. Threads 6 and on (including this one) are in the discussion section using its separate tag system. Also: 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17,18,19,20.
Spoiler Warning: this thread is full of spoilers. With few exceptions, spoilers for MOR and canon are fair game to post, without warning or rot13. More specifically: