I see what you're saying. It is unlikely but not altogether impossible IMO. I'm thinking more that Jessica *could* have just LEARNED about Deorr's fate when she became hysterical. Maybe she figured out or was told he was dead and that's what set her off. Maybe she had hurt Deorr, and he didn't "make it". To be clear, I think Jessica is very guilty in this, but I am puzzled that she would be so incoherent on the phone, on purpose or not, and then be so indifferent sounding on the 911 call. And if her hysteria were to convince TBC that Deorr had just vanished, why wouldn't she use that same hysteria to render her more believable to LE?
My strongest theory is he was never at the campground, and in a way, that's the saddest theory. Because it makes finding Deorr a needle in a haystack, and if he was found, so much time would've passed that COD and other details may be impossible to ascertain. Therefore, thwarting proper justice.