I have looked through ever mention of unbreakable vows in the fic and not found anywhere where this is made explicit enough for much confidence.
Of course it's possible that in-universe everyone knows that Unbreakable Vows survive death -- but it's far from obvious because surviving death is really rare. (And presumably no one has yet survived death using a Horcrux 2.0.)
"...so shall it be," Harry repeated, and he knew in that moment that the content of the Vow was no longer something he could decide whether or not to do, it was simply the way in which his body and mind would move. It was not a vow he could break even by sacrificing his life in the process. Like water flowing downhill or a calculator summing numbers, it was just a thing-Harry-Potter-would-do.
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 113.
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.)
IMPORTANT -- From the end of chapter 113: