This sounds somewhat like a worldbuilding question—you're working on a story of some sort, and are looking for some linguistic details to include. So I'm going to approach it from that angle.
"Proto-Indo-European", as it's commonly used, doesn't refer to a specific, actual recorded language. Instead, it refers to a sort of hypothetical reconstruction. We know that various languages are related, and probably descend from a common ancestor; PIE is our attempt to reconstruct that common ancestor. To use a biological analogy, we know that humans and chimpanzees had a common ancestor at some point in the past, and there must have been, at some point, a last common ancestor. We can even try to reconstruct what that last common ancestor might have looked like. But finding fossils of that single specific ancestor is vanishingly unlikely.
What's more likely is that we'd find documents written in a previously-unknown Indo-European language, either written down much earlier than anything we already have, or having branched off from the others much earlier than anything else we currently know about. Or even both! And, in fact, this has happened in the past—when Bedřich Hrozný managed to decipher some cuneiform tablets in 1917, and showed that the language on those tablets was Indo-European. The "Anatolian" languages, as they're now known, were written down a millennium before any other other Indo-European languages, and also split off earlier than any other IE branch. And, even more startlingly, they showed evidence of phonemes that until then had been purely hypothetical, Saussure's coefficients sonantiques (now called "laryngeals").
Could something like that happen again? Absolutely! It's not likely, but it's plausible enough to build a story out of it. There are even several as-yet-undeciphered scripts out there in the world that might turn out to encode Indo-European languages. And evidence like that might completely rewrite the textbooks on Proto-Indo-European. It might not be PIE itself, but for story purposes the effect would be the same.