As much as I liked Siuan, there really is nothing left in the story that she is needed for. I liked that change - though I should admit that I found Elaida leaving her alive in the books frustrating. I generally find it frustrating where villains in stories overpower, capture, then leave alive to escape, their opponents.
When Moirraine was channelling in the desert, my thought was she was providing a shield against Lanfear travelling into the area. Forcing Lanfear to engage her, rather than directly striking at Rand. Lanfear also wanted to since Rand had, in her eyes, rejected Lanfear and chosen to remain with Moirraine.
You're not the only one who assumed Lanfear did the shielding on Sammael. I assumed that too, just as Lanfear shielded Asmodean in the books.
We know that Semirag (sp?) is around in the background, probably with the Seanchan. It could be either one, but for sure Moghedian is dying along the way.
All in all, I *LOVED* this episode. The worst part of having watched it is not knowing yet if Season 4+ are happening. If anyone from the production team is reading this - consider this a plea for another 4 seasons.