In my opinion, the greatest argument in favor of Graendal being alive is pretty simple, though I dunno if anyone has mentioned it yet.

Graendal knows firsthand (through her experience with Sammael) that Rand does NOT ally with Forsaken (or any perceived enemy, for that matter). Were Rand to send an emissary to Graendal (as he did), she would know that he had no intention of talk or allegiance - Rand was letting the nobles know of his intentions, not asking for approval. That SHOULD have tipped her off immediately.

So Graendal receives a direct emissary of Rand in her, according to Rand and co., long-forgotten palace (though preciously known to all several books prior...). She Compels said emissary and, after an INCREDIBLY short amount of time, sends him back on his merry little way.

Iono... If Graendal is actually dead, then I... well, the Last Battle is already over.