I'm not taking about better or more accurate interpretations of ancient history. Out of all the ancient writings that have been lost from the Greeks and Romans, is there a chance that some might still be sitting somewhere waiting to be found. Much of the ancient histories that we have, source other works that are lost. I feel a sense of sadness every time I come across ancient history that draw from fist hand writings that would be beyond amazing to have access to. Have we ever found such works that were thought lost? what are the chances of that?
The chances of finding a more-or-less-intact copy of a "new" Greco-Roman work of history are very slim, I'm afraid. The last such text to be discovered was the Hellenika Oxyrhynchia, found in the first half of the 20th century, and that's still only fragments.
It is in principle possible that an intact mediaeval copy of some lost work is sitting in a shelf somewhere, maybe at Mt Athos or some monastery in Ukraine, but even if so, we've certainly got very nearly the entirety of what survives. Papyri are more promising, because there are always chances of finding a long-lost stockpile buried somewhere (however remote that chance may be); the flip side of that is that papyri are always in very, very poor condition, mostly scraps with just a few letters. Even so, when you have hundreds or thousands of such scraps it's often possible to make something of them. The Hellenika Oxyrhynchia mostly consists of two large-ish fragments.
But you're neglecting material evidence; and I wouldn't understate the importance of new analysis of old evidence either. For many aspects of the study of the Greco-Roman world, archaeology is far, far more important than historiography. It would be much harder to study things like ancient diets, demography, causes of death, and individual religious cults, without archaeology; and it would be basically impossible to study rural areas, trade routes and trade goods, and the lives of non-aristocrats. On the side of new historiographical analysis, there are many thousands of lost authors and texts that can be studied through the collation and careful analysis of fragments preserved in surviving texts. Just last year an important new edition came out of lost Roman historians (T. J. Cornell, ed., Fragments of the Roman Historians, 3 vols., Oxford, 2013). And it's always going to be possible to bring new types of analysis to bear, like the adoption since the 1980s of actuarial analysis to study ancient demography (relying on both historiographical and archaeological evidence). It's not as though there's a shortage of avenues of study to uncover new information!
You seem to be more concerned with textual sources, of which there is always a small chance that something will turn up. But don't forget material culture! Excavations are always turning up new objects that provide fascinating windows into what life was like in the ancient world.
And even if nothing new is "found" or "discovered," there is always more to discover about the texts and objects we do have. For example, the Antikythera Mechanism was found in 1900 and largely disregarded until it was discovered to be an incredibly complex analog computer in 2006. Studies of the device continue today.
This isn't from the ancient world, but another example that comes to mind is the Voynich Manuscript, which dates from the 15th century and is in a language that not even professional codebreakers are able to decipher. It appears to depict species of plants that are currently unknown or lost.
There is always a chance of something new being "dug up" out of the ground or found tucked away in some library somewhere. But the transfer of knowledge is often more complex than that, and despite the caveat at the beginning of your post, I would argue that "better or more accurate interpretations of ancient history" would prove much more fascinating and can spur academic debate for years to come, with or without the kinds of dramatic discoveries glorified by Indiana Jones and more popular history.