I do think the plot was ultimately Mab's.
The symmetry of Nic having to lose his daughter has to appeal to a vengeful, angry, bereaved Mab who has just lost one of her daughters (and all but lost the other).
However, Mab could not have DONE it. She indeed needed Kringle/Odin/Santa/Vadderung to coordinate with the other pieces in place. And of course, she needed Harry to do the job.
But ultimately, Mab is the one who puts real resources (i.e. Harry) on the line, while the rest only put trifles in (or in Hades' case, things meant to be put out there); Marcone cares for his people, sure, but it's not like his key pawns were in play; and Odin only shared some advice.
What is an open question to me is, however, how Uriel fits in. Was he running his own plot, because he literally has power and foresight beyond any of them? We know he is a spook one level up from Anduriel (Archangel versus Angel), and Anduriel is almost on the level with Vadderung, so that seems possible.
And if he wasn't but was just part of the plot, which of the plotters knew how to get in touch with him? Would Vadderung be mortal-enough to hang with him without cosmic consequences? Or is Mab close enough to his job description to be able to deal with him?
Or is Harry, as Uriel's mortal 'pawn' a sufficient interface?