If you took away the ticking clock and each person had thousands of years to write his novel, prove his theorem, or complete his masterpiece, would we continue to advance--or would we stagnate?
You also assume that a 1000 year old Einstein would still be Einstein. We have no idea what the impact on the brain of living that long would be. More than likely at some point previous memories would begin to fade away, and at some point you've replaced so many parts (memories) that there's nothing of the original left.
Additionally, society changes in large part because the people who make up society change. Would slavery have ever ended if older people hadn't passed away and younger ones with new ideas taken their place? Would we still be ruled by a thousand year old tyrant with a medieval morality?