My thought was that his personalized horcrux spell tied whoever it was used upon to the horcrux network he built.
Therefore, by using it on Hermione, instead of having two parallel horcrux immortals, Hermione's mind was connected to his network, and he was disconnected.
This was not something he had ever examined in detail, because it never occurred to him to spread his horcrux method around before.
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 111.
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.)
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: