Cast a spell on Hermione as a dead man's switch - something that will not permanently hurt/kill her unless Harry does something to incapacitate Voldemort and prevent him from dispelling it in time (not violating Voldemort's promise, since he does not expect Harry to do this)
He made a point to have Hermione alive in case Harry get out of the situation. It's no mistake that he doesn't.
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 114, and also, as a special case due to the exceptionally close posting times, chapter 115.
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.)