In my opinion, Master Xehanort ultimately gained control of Terra's body despite the conflict we saw between them in the secret ending. Through Terranort, who was now Ansem the Wise's apprentice, Xehanort wanted to fully give into darkness, even though he knew it would get rid of his heart. He believed that darkness was the ultimate power.
Perhaps "no heart" also represented how evil and uncaring he was. He didn't have any compassion for people, and did whatever it took to gain power, even if it meant stealing someone else's body.
Furthermore, I think his name also has the anagram "another" because when Xehanort became a Heartless, Xemnas was created. As Vexen said in Re:COM, Xemnas is "another ansem", meaning another form of Xehanort.