I'm fairly certain Will died/dropped into oblivion when Zero destroys and remakes their own Mirror World with Rhinne's power. I think it was speculated before that the one behind the Future Henesys/Perion was the dream manipulator Commander, who has yet to make his/her official apperance.
Spoiler
Actually I think musclewizard got it right.
And Hilla did say at the end that "You thought he would be destroyed that easily? Please, he wouldn't be one of us if he wasn't perssitant."