Now, I have read most of the theories and mine is definetly not as in depth as most of them but here is my theory. In the end of Crown of Swords it implies that Mat is killed by a building falling on him. My guess is that he is not dead. It is not actually a guess I would have to say that I am postive that he is not dead. Anyways, I think he will be captured by the Seanchan and be presented to the Daughter of the Nine Moons. My guess is that she will be around the same age as him. She will take a liking to him just as Tylin had but this time Mat won't mind. There is much more but that would take to long.