I dont think Mat will be punished, now that he is Prince of the Ravens. Whatever it means, it is obviously significant as it is the title of the Daughter of the Nine Moons partner IIRC.

Tuon said something about a punishment in either Crossroads or Knife of Dreams and around the same time said she always keeps her promises. That last part may have been in Winter's Heart, actually. She did mean to make him property once she was freed but that part at least seems off the table now. Unless you count the old ball and chain.. See, now I have an image of Mat as Andy Capp. I type too much.

He will loose/sacrifice one of his eyes to free Moiraine.