2 plot things left, Lomok and Ivarsa. I had Lomok be a social encounter with a combat fail state, since the party doesn't have any particular reason to hate him, and as mentioned previously he is one of the last remnants of what the BM were prior to Ivarsa. So if the party can come up with the right words and right rolls, they can sway Lomok and his retinue to leave. The combat encounter itself is kind of lame as written too, add some spellcasters.
Now, Ivarsa. Again, I gave her a chance to talk. Crucially, if she never talks, the players never find out that the worm is Pakano. The book offhandedly mentions Jesseri resurrected him, but is this reveal supposed to happen when they're talking with random witch lady that they are meeting for the first time? There's no prewritten dialogue for it. Once again, laaaammmmeeee.
So, back to reason for the demon temple: Pakano wasn't resurrected by a normal ritual and got fucked on a die roll to become a worm, Ivarsa purposely brought him back with a ritual that fuses demons with humans. It didn't work all that well, but so what? She got a magic worm mount, and next time she can do the ritual better than Jesseri did to get something more like Metuak.
In this way, Ivarsa is perpetuating the cycles that caused her pain in the past. Her family was all killed trying to make stronger warriors, and now she's unwittingly doing the same to others. Lomok doesn't know that the big worm is his grandson fused to a demon, but it's not a secret that will go undiscovered forever.
In the middle of the talking the devil inhabiting Ivarsa's brother's body comes in, and her facade breaks at the sight of her long dead family member. He starts talking with her, trying to get her to repent for what she has done, and right as she hugs him and starts questioning her decisions, the devil brings out a dagger and stabs her in the gut. This starts the fight, though the devil is content just to watch rather than actually participate.