my theroy is that.......she is only wiped from his memory because riku remebers her, so does namine,and also sora because maybe well really idk its kinda hard to explain over the computer.......(but i will try) *siff* *sniff* *deep breath* well here is an interesting thought from proof of the game...riku might remeber who she is because he is not a heartless nor nobody plus he spent alot of time with her. Sora remebers her because she is practicly part of him and the proof that he knows her is when he is getting his new outfit he says "Now the 5 of us oh i mean 6 of us can fight." or somewher close to that anyway he remebers her some how. Now for namine she remebers her because well she messed Roxas's memory to make her this was proven when you find out that xemnas says his way to obtain kh by haveing 2 keyblade weilders on his side. Now for Roxas, i belive when she was created she was made from his memory or body or whatever i don't remeber anyway ther for when he defeated her he gained everything back and it was like she never existed well for him any way...hope i helped buddy! this Steven Thibodeaus signing out for a job well done and a great question answerd.
LMAO that is a type oh ... my last name is THIBODEAUX not thibodeaus