The-Scott-Saviours

So, after I've watched FFPS's ending, one Henry's line kind of didn't sit right with me. Namely, the one where he says he remains in the building as well. I was surprised by it, since there was no indication of any other person inside the incinerators prior, and because I didn't really understand why he would do that (except obvious depression, but that explanation seems kind of shaky for me). Also, if he was still alive, wouldn't Afton and Co. have found them? Not to mention the whole age thing. Curious, I started thinking, how Henry could end up burning with a building in a way that was convenient to the narrative. And then it dawned on me.