I know that there are some artifacts that, using modern technology, can be recovered; but since I assume the majority of documents are long gone will our learning about the ancient world plateau, and has it already?
No, not at all. Even if we had recovered everything, there are always new frames, new interpretations, etc. that change how we see Rome.
One of the most important, and perhaps best, examples is Peter Brown's work. He argued the West never fell, but rather developed into a kind of society that suited its historical circumstance with little material change beyond the aristocracy. That was in the 70s, and his conclusions are disputed, but widely accepted. It's a locus of the continuity or change debate that happens in pretty much every field now. Change is the traditional view; Brown basically started the continuity view in this particular case.
Archaeology continues, as does museum studies. I've done work on the Ludington Sarcophagus at the Santa Barbara Museum of Art, for instance. We didn't learn anything new about Rome in that project, but we learned how people in the past reused Roman artefacts, and how that particular sarc got to Santa Barbara.
There's an excavation of a villa going on in Scarborough in the UK. The American Academy in Rome has a ton going on in Italy.
As for texts, it's rare, but every now and then something pops up. Cicero's de Re publica we knew about from Cicero's letters, but the text was lost until something like 1810. Some idiot monk tried to erase the text and used the velum for something like a hymnal. It was only in the 19th century someone realized there was an underlying text. It's pretty well in tact, actually.
And then we have more papyri than we can handle. There's too much papyri that survives for the papyrus scholars to handle. But in 2012 we got a new Sappho fragment. While that's Greek and not Roman, it demonstrates the possibility that there's something still out there if we bothered to spend the time and money to look for it.
So there are plenty of ways our understanding of Roman history can still change. New models. New interpretations, and yes, even new evidence.
u/LegalAction Gives the widest response - there is still so much more to find, especially with archaeology, and there is still so much to re-interpret, or interpret more deeply. But here's another fun tidbit for how much more there is to learn in just one way we learn about Rome - ancient texts:
A sizeable number of extant Latin texts, and an enormous number of Greek texts have never been translated into a modern language. (The Greek texts I'm talking about in this context were primarily written in the era of the Roman Empire, not ancient Greece). A lot of Roman historians do not have a fluent grasp of Latin or Greek, and have no interest in trawling through tomes and tomes of nonsense to find the diamond in the rough. Many of these books remain untranslated because the likelihood that it's worth the time investment is small, and researchers have far better things to do with their time then spend their entire career hoping they can luck out and find a winning lottery ticket. That means there's huge troves of information on Rome that could fundamentally alter our assumptions that has either never been read, or if it has - never been read by someone who was also aware of the academic claims the primary source refutes.
This is something AI will help with in my lifetime.
When this academic technological revolution comes what we previously understood about Rome is going to be meaningfully altered. We haven't even begun to reach the limit of what we will know about Rome.