RJ came up with this "elegant" and quick way to get rid of the clever Graendal by Rand's use of brute force. I really don't see what the point would be, if Graendal somehow managed to survive, is still around and Rand has to come up with an even better idea to outsmart Graendal. Seems like a pointless twist, which further burdens the plot.

Graendal's PoV in the prologue also wasn't redundant, because it gave us e.g. more clues about Moridin's plans and situation. It also explains why Graendal didn't dare to immediately flee from Arad Doman, when Rand arrived. She had to stay and make contact with him eventually.

BS indicated as well that Graendal is dead by saying that she will just be mentioned a few times in ToM, and that ToM will make it clear, if she is dead.

Besides this, Semirhage's and Elza's ter'angreal bracelets remained, when Rand hit them with balefire on the chest. Considering this one wonders, if Graendal's angreal was even balefired, since Rand just aimed at the palace.