looks like he transcended like Akira did. the proccess seems destroyed his already out of control body from this world,thus removing his physical connection. I don't know for sure though
In the words of Dillon from the extended version of Alien 3, "Those that are dead are not dead. They have moved on. They have gone to a higher plane."
The same can be said for Tetsuo. He's not dead. He's simply moved on to a higher plane.
What do you think?