Thing is, we know just one thing - nothing else - and that one thing is: there will be no deaths (if we're to believe DPC).
What we know it won't happen are NTR and incest - cause those are "no-no" things for DPC (again, if we can believe him).
Everything else is a possibility. And we're going back to that question without an answer: "What DPC considers dark/unsettling enough to warrant those warnings on the start screen?"
It's funny that NTR, if used in the correct way, as in a way to cause drama, desperation, jealousy and depression, is a huge dark element that can cause people to cry. It is done in some Japanese visual novels, but it has never been done right in any Western story.
I remember playing Boku no Kanojo wa Gatenkei (a Japanese visual novel) and crying during the sex scenes, instead of fapping to them. After finishing it, I spent almost a month without playing anything new because of how deep it impacted me. Also, in Japan, when it was released, it was reported that more than one hundred players started a mental treatment because they got into depression after playing it.
I really don't see the huge issue people have with NTR and characters' death. They can make for good story elements. I'm liking BADIK, I loved AL and I just want to see the story DPC wants to tell. So far, I'm very satisfied with what he has done and I'm happy to support him.