Oh, I disagree!
If Socrates had died a natural death a few years later — he was, after all, seventy years old — would Plato have been so incensed at the injustice that he abandoned his career as a playwright and instead devoted himself to recording the thoughts and arguments of Socrates?
And if Plato had not turned to philosophy and founded the Academy, what of Aristotle? And if Aristotle had not tutored young Alexander, then would he have become Great?
Without Plato, it is hard to imagine Plotinus, who provided the model of the Trinity when Rome embraced Christianity.
Socrates certainly had his ideas and his methods, but I would say that his execution sparked his legacy, not ended it.