Punishment isn't always death. Galina was taken by Thereva to the waste as a gai'shain/slave. Elaida was taken by the Seanchan to be a damane. Colavere only had her property and titles stripped from her (though she did hang herself after). Sometimes the best way to punish those who sought power and control is to take away their power and enslave them. I don't know that we'll see any non-death fates for the Forsaken, but it's possible they might live out a life of suffering. I'll be surprised, though, if any get to go off on their own to scheme and twirl their mustaches.