Similar questions on how much ancient literature has survived have been asked before, but these questions were more vague in their definitions. My independent research has found partial answers that have helped me to specify this question:
This leaves open the period when virtually all the Greek world was under Roman rule: the entire New Testament, Galen, Ptolemy, Diophantes, Josephus, Cassius Dio, Origen and others. How many Greek words have survived from authors born after 100 BC, and died before AD 500? My access to libraries is restricted now for obvious reasons, or else I would have searched for the Bestand und Überlieferung der Literaturwerke des griechisch-römischen Altertums; as the Thesaurus cited by Bagnall contains, as of now, some 120 million words and seeks to compile all Greek literature down to the Turkish conquest, this sets an upper limit of 110 million or so, but doubtless most of this figure is Byzantine. How much of what is extant is from the Roman period?
I can say more and fill out my answer to you as needed, but as it stands my answer will be short. You might be interested in the manuscript tradition of the Greek philosopher Plotinus, who is the only philosopher from antiquity besides Plato whose works survive in full. It is that fact about him that makes him relevant to your question.
(Historians of philosophy usually count some philosophers from the period you are considering as medieval, not ancient, so I am excluding them here, but even major "medieval" figures such as Augustine and Boethius don't have their works survive in full. And besides, their writings aren't Greek.)
Porphry is another major philosopher whose Greek writings have survived -- but only partially. Same goes for Iamblichus and Proclus, but the latter died in 485 AD, so he is nearly pushing the boundaries here.
For a great study of Plotinus' manuscript tradition, see:
Henri D. Saffrey, "Florence, 1492: The Reappearance of Plotinus" Renaissance Quarterly Vol. 49, No. 3 (1996), pp. 488-508