I'm also leaning heavily towards "Ardbert" just being his missing body under Elidibus' control. I don't think they'd specifically mention that it was never found in the role quests if it wasn't going be something of importance.

What exactly he intends to accomplish at this point is anyone's guess. I don't think he'd try to stop us head on since as far as we're aware the only thing that made Ardbert very special (His soul) is gone now; unlike Zenos who was subject to all the manner of experiments on top of Garleans just being physically strong.