I actually quite like Zack Snyder, although it must be said that if he wants to make Standalone stories, I strongly suggest he just consider doing the books that aren't based on Jedis. It would be a refreshing take, I think. Sadly, I've never read any of the books, but a Zack Snyder helmed Shadows of the Empire would be pretty cool, and my knowledge of SotE is based solely on what I remember of the N64 game.
I think regardless of Man of Steel succeeding or not, though, I don't think Snyder will want to take over Star Wars, really. I have the feeling his acceptance of it would be the same as Quentin Tarantino's to some degree.
Still, I'd probably watch it.