IMHO I think the Dark One means to dispose of the Forsaken once they accomplish what it wants. It's called the Father of Lies for a reason, and they are deluding themselves if they think the Dark One would be satisfied letting them rule in It's name.

Moridin laughed again, the same heartless laugh as before. "Perhaps you will," he said. "But do you think that matters? Consider it. The Wheel turns, time and time again. Over and over the Ages turn, and men fight the Great Lord. But someday, he will win, and when he does, the Wheel will stop.

"That is why his victory is assured. I think it will be this Age, but if not, then in another. When you are victorious, it only leads to another battle. When he is victorious, all things will end. Can you not see that there is no hope for you?"

"Is that what made you turn to his side?" Rand asked. "You were always so full of thoughts, Elan. Your logic destroyed you, didn't it?"

"There is no path to victory," Moridin said. "The only path is to follow the Great Lord and rule for a time before all things end. The others are fools. They look for grand rewards in the eternities, but there will be no eternities. Only the now, the last days."

He laughed again, and this time there was joy in it. True pleasure.