Actually, any way you slice it, I think Corvo is the ultimate winner here. His Blink ability + Wind Blast spam (if he can pull this off) should batter Hei like a rag doll and give Corvo the win.
I'd like for Hei to win, but I don't know how he'd pull it off. His electricity needs conductive media to be discharged, I believe, and I don't know how Hei is going to manage to hit Corvo with it when he's teleporting about on a whim.
Does Corvo have some sort of mana bar that limits how many times he can use a particular power in the game? If so, you may have to include some game mechanics-based restrictions for Corvo here.