OK so like Xemnas's confirmed real Heart should have totally gone to Xehanort upon Recompletion like EVERY NOBODY DOES, RIGHT?! So why did he need to be brought from the past instead of just extracting him from the PRESENT Old Nort? Roxas and Namine went back properly, even XION went back to Sora, so why didn't Xemnas go back to EITHER Old Nort OR even into Terra's Heart? He should have, by all natural laws! It didn't need convoluted time travel. Only for Ansem SOD! I feel like Nomura seriously overlooked this here. Even Lea and them's Hearts went back to and merged with their Somebody's Recompleted selves Hearts...

Xemnas should never have needed time travel to come back when he should have gone back into Old Xehanort and/or Terra for him to just pull out THERE!

who says he heart survived the end of KH2

Ansem the Wise said that Sora was the only one able to return to his human form without destroying his Nobody. I believe this means that no other Nobody is able to co-exist with their Somebody without using time travel, except Namine and Kairi due to the fact that Kairi never lost her human form and Sora was involved in creating Namine. Also, I think that with other Nobodies who possess hearts but then return to their human form, their Nobody hearts merge with their human hearts to become one and the same (like Axel/Lea). Therefore Xemnas couldn't be extracted from Xehanort without Xehanort perishing. 

The heart that Xemnas grows went to Old Man Xehanort when he was killed in KH2. This is because Xehanort's Heartless/Ansem Seeker of Darkness was also dead by then, thus allowing the return of the original person/the Somebody. This is why both Ansem Seeker of Darkness and Xemnas had to be plucked from either other timelines or a point in the past of the main timeline when they still existed individually from Old Man Xehanort himself.

There's actually more fishiness surrounding the other members of the organization returning to their original selves (Minus Roxas and Namine who were special cases, and Xion who was a different kind of special case) than there are the two halves of Xehanort. We never see their heartlesses destroyed only their nobodies. We just get left to assume that their heartlesses were killed by some keyblade wielder or another over the course of the adventures leading to KH3. 

Edited October 23, 2024Oct 23 by FadedSparkle