But I think I just lost half my evidence with one sentence: “True death for Northman is true death for Northman.”
It wasn’t until Roman said that that it truly hit me: Despite the fact that Bill wanted Eric dead and was the one to recommend his true death in season 4, when he didn’t follow through on it, he was going up against the Authority. Eric has to have realized that as soon as he got his memories back: Bill really did save his life and put himself at risk doing it. So, yeah, it does make sense Eric would feel like he owes Bill loyalty.
But I still like my theory for fanfiction. 🙂