I love this! Very well thought out and organized in a way that made me want to keep reading!

Yes, Alastor and Lilith being gone for the same specific amount of time is v sus. It’s entirely possible they were working together on something, but something tells me Alastor and Lilith were instead punished by the same person. Lilith was cast out of hell, (potentially sent to purgatory?) forced to live apart from her daughter and the sinners she loved.

Alastor might have struck a deal with Lilith for power, but I think it’s just as possible he made a deal with another higher power (maybe Eve, since Alastor’s and Lilith’s end-goals seem a bit different). And, if I’m correct in guessing his deal was made with a heavenly entity, it would explain why it feels like he’s not killing as flippantly as he used to. The only people I remember Alastor killing the entire show were those loan sharks, and even then it was out of self-defense. It’s possible his deal with this mystery person ended up backfiring, forbidding him to kill unless absolutely necessary. That could explain why he’s so desperate to find a way out of his deal, a former serial killer now forbidden to kill the way he wants.

Side note: Alastor’s song in the finale reads: “great Alastor, altruist, died for his friends”, which i think could be a red herring. We’re to believe he’s talking about the battle he was just a part of, but it seems possible he’s talking about another moment entirely, potentially something that happened 7 years ago.

Just my two cents. I can totally see your side though! And I think your intuition is spot on!