Board Thread:Questions and Answers/@comment-7112041-20130311201124/@comment-61022-20130325222207

Technically, the Hulk is an aspect of Bruce Banner's personality, he's not a separate entity per-se. Heroes Reborn was not the first time Banner and the Hulk were separated either. It was done previously in Incredible Hulk Vol 1 #315.

Each time they have been separated it was something that would have proven fatal to both since they two halves of the same person. The first time it did not have much of an impact, but in Heroes Reborn the fact that they were fractured between dimensions caused the impending cataclysm that was threatening the universe in Heroes Reborn: The Return (and the reason why the Celestials demanded the Franklin Richards choose which Earth lived or died)

But the purposes of clarity, Hulk and Banner are considered the same person (even when they have been physically separated) It avoid's confusion and these separations are always short lived.