I mean it's not really that vague anymore, tbh. Noriko seemed to more or less explain it the update prior, and Maya herself seems to support it:
So, Random Theory Time: Noriko and Maya's deal, may have broke an already broken Sensei:
As for why Maya still avoids the Old District after all this time:
I think it's likely for the same reason she remains a shrine maiden:
She doesn't want to risk breaking the deal in case it influences her survivability.
I struggle to see Sensei choosing to abandon the Nakayamas considering how quickly they've become important to him. Even ghosting Niki wasn't really a choice. He seemed barely functional, had just lost someone he loved, and had a kid to take care of. Dating likely wasn't really on the table, but considering how jealous of Niki, Maya is:
Without ever actually meeting her, I think it's fair to say Niki was the biggest threat for Sensei's heart, in Maya's point of view, just based off what he's likely said about her since ghosting her.
Tbh, I think the only people more or less confirmed to have abused Sensei is Maya and Sekai. I could see Saki trying to forcibly indoctrinate Sensei, since she seems actually religious and didn't like Sensei much though. Ami tried to give herself to him sexually, but he didn't want her apparently:
If Ami wanted to take advantage of him sexually, then she'd probably have multiple kids by now, or at least wouldn't optionally still be a virgin.
Also, I think the Shapeshifter being a teenager and a shapeshifter from the future is a little bit weirder than her appearing in the Happy Event, tbh. I mean, based off her recent talk with Ayane, if she is Ayane's daughter then Ayane apparently will eventually have her one day:
Which seems to imply that the child Ayane lost, isn't meant to be the Shapeshifter. Perhaps a sibling though.
I've actually been wondering if Ayane's "unnamed baby" might have appeared elsewhere:
Honestly, I wouldn't be surprised if most of these supernatural things end up being revealed to just be Sensei's kids from various timelines.