Can't tell by your phrasing here whether you're aware of this or not, but no use of a Time Turner in canon altered the timeline, either. Everything that Harry and Hermione did while time-turned was exactly what the trio saw the first time through. That part of HPMoR's time travel rules are identical to canon's, just more thoroughly explained.
Yes, that's what the (apparently) was for. The point is that this is a canon example where a character thought someone was dead and used a Time Turner to rescue them, but the timeline ended up working out so that they were never dead in the first place (as it had to).
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 88-89. 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.
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: