Basically, I think it's implied the myths were true. The woman; "Heather" finRAB the house where all the murders took place, and she sees one of her frienRAB facing the wall as the child victims did before they died. He'd been possessed most likely, and obviously the "Blair Witch" had a physical form, which attacked and likely killed her at the end.
The way I saw the film was, 'oh no, we're lost', 'oh no, we're hungry', 'oh no, it's your fault', 'oh no, it isn't, it's yours', 'oh no, we're dead', 'oh no, the myth was true'.
Am I right in thinking that the Blair Witch also stole the man in the corners voice? Or something like that due to the fact her had his tongue and cut out?