He said that he didn't want to reveal, if LTT's voice was just an imagined construct, or if LTT's original personality did truly appear in Rand's mind (e.g. provided as a kind of guide by the Pattern), since RJ also didn't want to reveal this (but apparently the answer is in the notes):
"Jordan was intentionally vague about the issue of Rand and Lews Therin’s one soul and what part madness played in the two identities."
And: "Robert Jordan never really intended to clarify on whether Rand is hearing Lews Therin because he’s insane or if he’s really there."

I find it a bit hard to believe that one can simply cure yourself from an imagined voice, if it is a part of your madness. Therefore I tend to think that the voice was real and vanished after it wasn't needed anymore.

Besides, the scene on top of Dragonmount was apparently a bit like what happened above Falme, namely in some ways an effect of the Wheel helping Rand to integrate LTT:

"I asked him if Rand’s access to the infinite lives while on Dragonmount at the end of The Gathering Storm was the Wheel getting involved directly.

He replied as follows, according to my memory, that there was a Pattern Level Event there, but it wasn’t specifically the Wheel giving Rand access to memories his previous lives. Brandon asked for some clarification about how Jordan explained his answer at DragonCon. We were rushed and I could not give him that direct quote, so I was unable to ask more specifically if Rand was seeing the soul’s history of lives lived, or if more generically the Wheel displayed to his mind a series of previous generic lives, like it displayed Rand and Ishamael in the sky above Falme. He did speak briefly about the Wheel not physically 'touching' Rand and/or Ishamael, which seemed to be suggestive of his initial response that it didn’t 'touch' Rand’s mind to give him access to his own memories. Once again, a more detailed discussion of this subject is worthwhile, especially one recorded."