Shara stuff with Demandred was hinted at early in book 6.
Sammael and Greandel are talking about other forsaken. Sammael is talking nonsense about Demandred. Greandal tries to give hints about what Demandrad is actually doing by showing Sharan rulers she kidnapped. Later we see her POV. She complains about Sammael being an idiot and not getting the hint.
I don't know when RJ decided to separate Taim and Demandred. But this is book 6, and both characters are introduced in this book. So Demandred would be in Shara regardless of readers guessing Taimandred.
As far as I understand, Taimandred was an idea RJ had, but he never committed fully. He wrote Taim and Demandred separately with a possibility to combine them. Not the other way around.
Only reason i have is Lan. He needed a moment. He was one of our original characters leaving Emonds field. It was kind of a fan service. Also Gawyn and Galad needed plotlines. I can see Galad having a moment with whitecloaks. Maybe a redemption plot for whitecloaks. But Gawyn was a mess. Demandred functioned as plotline generator for male swordsmans 😄
I don't get this why people hate how Sammael died.
Chronologically. (I think)
Balthameal—killed by an ordinary tool used by Age of Legend farmers
Aginor—Burned with too much power
Be'lal—instant surprise attack
Ishamael— Ok, this was good but confusing.
Lanfear—Tackle
Rahvin—Again, ok in the sense that it was a struggle, but POV changes made it hard to follow.
Asmodean—🙄 No comment.
Arangar—Friendly fire
Osangar—Bound and left to die
Semirage— Surpriseeeee! I have True Power
Messane — Same with Rahvin and Ishamael.
Greandal—Punishment
Cyndane—Snap
Moridin—final battle, no complains.
The rest of them are alive I think, if I didn't miss one. I think out of these, Demandred would be in my top 3. Sammael would be in my top 5.