The answer is yes and no. It all depends on your personal beliefs (for this example anyway).
If you believe in fate, then yes, he would have broken it anyway. To explain this answer will require a little more in depth explaination of fate.
Fate (explained pseudo-scientifically) is a series of chemical reactions. And they all started millions of years ago. Every chemical reaction leads to another and to another and to another. So what you do today is just a reaction a little farther down the line. You are going to do it no matter what.
I won't claim to know what you believe in if the answer is no. If the oracle had said nothing to him, then he wouldn't have moved, and therefore wouldn't have broken the vase.
But she DID say something. She saw it happen before it did. So the real question here is why did she say anything?