A good question. Did you know there's a theory, later on disproved of course, that says that anything that can happen will happen, if not in this universe then in another one. But that's just silly because that would imply an infinite number of universes, and nothing... nothing is infinite. Well, almost nothing, but most certainly not universes.

You see, we are so small, that the universe, in our eyes, seems limitless. While there is, in fact, an edge to our universe, there must also be a limited number of universes in existence, constantly contracting and expanding, changing, and therefore that means there is a limited number of things that could happen.

Anyway. [ shakes a hand as if to clear his mind. not that ever works that well, it's always a mess in there ]It's more than likely to be at least one more version of us... somewhere out there. Maybe in another reality there is a Clara whom I never got to meet. Or a Clara in a place where there is no Doctor.