Out of all plotlines, it seems that Great Purge in the White Tower kinda puts an end to the White Tower cleansing story lines. I doubt we'll see anymore cleansings in the Tower in the next books.

The other Forsaken:
1) Ishamael should die with the Last Battle. It seems logical conclusion;
2) Demandred likely dies in the battle. He tied to LTT with his story line, but he also ties to Mat as opposite General. It also seems logical that Shadow General is defeated at the end;
3) Aran'gar is likely to die at the hands of Narishma. First of all, there is foreshadowing when Rand teaches him balefire. Second of all, Narishma seems pretty pissed of at her/him;
4) Cyndane has unfinished bizness with Moraine. It also seems that she has unfinished bizness with our Avi and Elayne. I think it'll go to the final lethal conclusion at the end;
5) Moggy has very unfinished bizness with Nynaeve. I don't think Moggy let it rest;