First of the Fallen was a favourite of Gods, and only he can unmake something entirely. But I'm just going by what I'm reading Zoat has said about the effects of the sword. In this story. If I'm wrong, I'm wrong, but that's how I'm reading his description of the sword.
No, that's the in character explanation used in the comics- That the First of the Fallen was reincarnated by God after being killed by the blade.
In this fic, the in character explanation as used by Paul the SI was that while the blade can kill anything, at a certain level it can't keep it dead- Resulting in reincarnation.
Zoat has never given any indication that Paul is incorrect on that account, and barring that, well as Zoat's self insert it's generally a good rule of thumb that Zoat will have a similar view on how things should work, and Zoat is the one writing the story.
For example, Paul was presented as thinking that wearing armor is a no brainer. Zoat didn't have Paul find out he's being wrong genre savvy with the revelation that armor is useless because it's not the rules of physics that determine who gets hurt but the rules of narrative causality.
Which, what with the time tailors, destiny's book, the Overmonitor, and people with author powers like Grant Morrison showing up in Animal Man and Doom Patrol, is lets face it closer to the truth in the DC franchise even if you don't want to really break the fourth wall.
Ditto with archery being a silly basis for a superhero. Using physics, absolutely, using narrative causality, it's good enough for the Justice League, Apokalips, New Genesis, and 853rd century Earth.
Which leads to the conclusion that Zoat wasn't interested in writing a story about an SI of his quantifying narrativium like he's in Ankh-Morpork.
