It wouldn’t be RG Sylvanas, the RG would be the blue eyed undead HE we see today. The Banshee Queen(the one responsible for the atrocities) would be an entirely new being manifested from the dark magic used to fracture RG Sylvanas soul.
I think that destroying that manifested(cloned if I may) entity would sate some fans thirst for blood. I don’t think killing Zovaal will sate that thirst.