After this event, Tetsuo says the following:"I am Tetsuo.".
Like Akira, Tetsuo has accepted his role as a superior being;
I am Tetsuo" is a great and memorable line,
but albeit a tricky one to decipher.
So, having never read the manga, because I am a cheap jerk or whatever,
I feel that Tetsuo dies.
Not as part of Akira or as a new merged entity, but as Tetsuo in one form or another.
Tetsuo manages to gain full control over his powers,
and these abilities end up creating a new Big Bang in another dimension.
I believe that Tetsuo had created a new world to inhabit as a higher power
and not in a firey passion but in a benevolent society.