I'm enjoying the story; but am bothered by this passage:

The Dementors were coming.

"My Lord, you - you should not risk yourself for me - take back your Cloak -"

"Be silent, fool," hissed an angry voice. "When I decide to sacrifice you I will tell you so."

She's got a valid point, said Slytherin. You shouldn't risk yourself for her, there's no way her life is as valuable as yours.

For an instant Harry considered sacrificing Bellatrix to save himself -

Bella's life isn't just less valuable than Harry's. Her life has a large negative value. Harry should be trying to prevent her escape. This righteous, humble talk about why Harry can't save himself instead of her is exactly the sort of thing that makes me so exasperated with comic-book superheroes; and just the sort of thing I was hoping the Methods of Rationality would expose, or at least avoid.

It does work out better than if Harry had tried to save himself - but, it's a story. This story is remarkable partly because it uses a rational protagonist; but it could also be remarkable for making more concessions to reality than most stories. This is a case where it failed to make a concession.