The rest of the quote you've referenced is very clear on the consequences of the [Dementor's Kiss][1].

> *"You can exist without your soul, you know, as long as your brain and heart are still working. But you'll have no sense of self any more, no
> memory, no...anything. There's no chance at all of recovery. **You
> just - exist. As an empty shell**. And your soul is gone
> forever...lost."*

It looks pretty clear that a human without a soul will endure in a coma, a form of [persistent vegetative state][2].


  [1]: http://harrypotter.wikia.com/wiki/Dementor%27s_Kiss
  [2]: http://en.wikipedia.org/wiki/Persistent_vegetative_state