I don’t think “It was not a vow he could break even by sacrificing his life in the process” means what I think you may think it does.
(I think it means something like “Harry can’t, and won’t, say ‘Oh, screw it, I’ll destroy the world’ at the price of dying. He simply, will not make any choice that in his judgement risks destroying the world”. Note that this leaves entirely open the question of whether anything could release him from this constraint. Of course the word “Unbreakable” in the name is something of a giveaway; but I am not aware of anything in either canon or HPMOR that rules out the possibility that such a vow is somehow tied to the vower’s brain, or ceases to exist on their death for some other reason.)
I don’t think “It was not a vow he could break even by sacrificing his life in the process” means what I think you may think it does.
(I think it means something like “Harry can’t, and won’t, say ‘Oh, screw it, I’ll destroy the world’ at the price of dying. He simply, will not make any choice that in his judgement risks destroying the world”. Note that this leaves entirely open the question of whether anything could release him from this constraint. Of course the word “Unbreakable” in the name is something of a giveaway; but I am not aware of anything in either canon or HPMOR that rules out the possibility that such a vow is somehow tied to the vower’s brain, or ceases to exist on their death for some other reason.)