If she doesn't, I'm sure (hope) we can find someone else, I just happen to believe she is the best candidate and most equipped to take on and beat Obama.
If she stays in her current position, she will still influence American politics as one of the top few commentators for many years, and whoever she endorsed would win the nomination and beat Obama.
It's a big decision, I have no idea what personal matters and thoughts she is putting into making the decision. I can speculate, but that's all it would be.
Surely, you don't believe that she'd leave the American public in the dark so long about something as important as this, do you? That would be completely out of character for her to do that. She's made of much better stuff.
What makes sense, is that she knew this question would hang over the Republican primary, and that she would have answered it quickly if she had the slightest doubt about running.