To be blunt, if she were dead, dogs would have found her by now.
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Loved reading your insight, Snow. I'm not sure I agree with this point, though. I can think of quite a few cases when a missing person turned out to have been dead for quite a while, and dogs weren't the reason that person was eventually found. In most of the cases I'm thinking of, dogs were used at some point, but the location where the body was later found wasn't near the place where anyone was searching.
Think of the Morgan Harrington case, for instance. I don't remember the details about whether or not dogs were used, but tracking dogs would have only tracked her scent to the bridge, and I don't know if the kind of trailing dogs that are used for scents in cars were ever used. Also, cadaver dogs obviously didn't find her on Anchorage Farm, so if they were used it either wasn't an area that was searched or it was searched before her body was placed there.
To say that the dogs would have definitely found her by now if she were dead, we'd have to know the details about what types of dogs were used, exactly where they searched, and frankly, where Holly is, which of course would mean she's no longer missing.
I'm not trying to be argumentative, because I do see where you're going. I believe Holly's not far from home, whether or not she's alive, but I just had to make the point that we have no idea what happened, she could have gotten on a plane and been killed somewhere else, etc., in which case dogs used in Darden/Parsons wouldn't have found her (I don't think she got on a plane, just an example scenario).
I see your point that IF she were dead in the area that was searched, the dogs likely would have found her. However, we don't know where she is, so she could be dead somewhere else, and we also don't know the details of what kinds of dogs were used where, so she could unfortunately be dead near hometown, and if dogs weren't used in the right area, they wouldn't have found her.