This may seem an odd thing to say, but part of me hopes that it was an accidental death in the apartment that was covered up because I think the other option would just be so awful for Madeleine. I don't want to even think about what horrors she’d have endured.
Whatever did happen to her, I agree she was failed by so many people.
I wonder about the possibility of stolen to be sold into illegal adoption and having her real past hidden from her... but now she's an adult and we have internet and 24 hour news, I doubt Madeleine could be alive as an adult and not find out who she is and come forward if able.
So I, too, "hope" she died very quickly and there was nobody else involved.
I go back and forth on Kate and Gerry but common sense tells me there is just no way they could have got away with it all these years. While you do get criminals who hide in plain sight, the McCanns surely became simply too infamous too quickly to pull it off? I also don't believe at all that they would have harmed her on purpose beyond the neglect, it would have been some sort unforseen circumstances and then they panicked.
Mostly I feel like she got up looking for her parents, had an accident and died. Still awful but not like being taken and held by someone like CB would be.