(The HPMOR discussion thread after this one is here.)
The previous thread is over the 500-comment threshold, so let's start a new Harry Potter and the Methods of Rationality discussion thread. This is the place to discuss Eliezer Yudkowsky's Harry Potter fanfic and anything related to it. The latest chapter as of 09/09/2011 is Ch. 77.
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: one, two, three, four, five, six, seven, eight. The fanfiction.net author page is the central location for information about updates and links to HPMOR-related goodies, and AdeleneDawner has kept an archive of Author's Notes.
As a reminder, it's often useful to start your comment by indicating which chapter you are commenting on.
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:
You do not need to rot13 anything about HP:MoR or the original Harry Potter series unless you are posting insider information from Eliezer Yudkowsky which is not supposed to be publicly available (which includes public statements by Eliezer that have been retracted).
If there is evidence for X in MOR and/or canon then it's fine to post about X without rot13, even if you also have heard privately from Eliezer that X is true. But you should not post that "Eliezer said X is true" unless you use rot13.
I'm pretty sure something more literal was meant. The way the story is written, it sounded like Harry was in danger of dying from exhaustion, expending... something, to fuel his Patronus. And expending irrecoverably, it is stressed, so it's not like he just did the equivalent of a life-or-death sprint which made him really tired.
I see no indication that the thing permanently sacrificed was the same thing fueling the Patronus. I think the Patronus burns "life" in the sense of one of the things Dementors also suck out, but that can be regenerated by resting (it was implied that the prisoners in Askaban would partially recover magic and something else if the Dementors didn't keep sucking it out when the true Patronus gave Bella a weeks worth of such regeneration back), and it seems unlikely that such a loss to Patronus radiation would be more permanent than loss to Dementors.