I had to go with Granamyr.
I've always thought of Granamyr as one of the most powerful beings in the MOTU mythos. If Shagora had attacked Darksmoke instead of Grayskull, I think Granamyr would have defeated him. Probably with the help of He-Man and some other heroic warriors.
The second scenario is pretty interesting. I'm not too sure how that would play out.