He will appear in the same state, his heart fell in darkness --> Xehanort (not the Master, not Terra, or somewhat else)
And what does it have to do with Lea? I wrote it above. Read it again and if the preconditions are like i listed he will appear as Lea.
If you don't know about, read the DRS XIII
XtA is made from, Terra, MX's heart and ME's heart. 3 Hearts, 1 Body. Not 1 Heart.
We don't know if those hearts merged or if they even can.
So, when XtA fell to darkness, we have no idea how the separation went.
For all we know, there might be another "Xehanort" running around that appeared when XtA fell to darkness.
We only know where two of the pieces went.
MX went to Ansem SOD.
Terra's body went to Xemnas.
Whether Terra or Eraqus are in unknown. It's quite possible they were in Ansem SOD or even Xemnas,
but we don't know for sure because it's not the usual circumstance because
XtA wasn't a normal person. (Lea can't even be used as a example because, as far as we know, he's normal)
Also, we have that Voice in the Chamber of Repose that is still unidentified. It's possible that it could be Terra or Eraqus.
Lea is not in torment, Axel is. And please, give me a link to whatever DRS XIII (I assume it's an interview), because I never even heard of that, and Google hasn't either.