@NEETzsche @caekislove Actually I did. I made multiple posts addressing that exact scenario, although we were talking about New Testament reliability, I don't know why you're bringing up Gnostic texts again.

Monasteries preserved heretical texts literally all the time, even banned books. That's why we still have the writings of Pelagius and the Infancy Gospels, for example. If the Gnostic books were relevant in the Christian world at large, at least a few copies would have survived, if only in remote places like Armenia.

In all probability, they were lost because they were irrelevant. That's also why only a couple of Gnostic writings are even referenced in polemical literature. No one knew about them. They were just obscure little tools created by grifters and discarded when they weren't useful anymore.

Manichaeanism also rose to popularity in the Empire at pretty much the exact same time as references to Gnosticsim decline. They were probably absorbed. They propose a similar worldview.