This is how I read it, anyway:

There's no doubt in my mind that the LTT voice was "real," in the sense that it knew things that only LTT could have known- weavings, personalities, references to AoL things that only the other Forsaken know, etc.

I also don't doubt that hearing the voice was either a symptom or a cause of Rand's continuing madness. His mind, quite literally, was fractured.


At the end of tGS, Rand had his epiphany- he, and LTT, and all the rest of the Dragons, were the same soul. In that realization, his mind was healed (at least mostly). He stopped fighting to "win" over the LTT voice (or giving in to despair and "losing". Now he's just Rand, the Dragon, who has always been the Dragon and always will be.

I wouldn't be surprised if he became something like a subtler version of Mat and his memories- having the knowledge of certain things not from his own life, but still completely able to function as Rand al'Thor, instead of being possessed by a dead man, or acting as a hive mind.