Elaine Pagels straight up lied about the contents of Athanasius Letter 39, turning an admonition to only use certain canonical and apocryphal texts for teaching and a warning against similarly named heretical texts (like most of those found at Nag Hammadi) into a command to destroy everything except the canon and the apocrypha. Since she was one of the early scholars to work with the Nag Hammadi library, her hiding-to-avoid-destruction theory remained influential for a long time, despite it being based on a lie. More recent scholarship tends to theorize that these texts were a burial deposit—a practice that began long before Christianity in Egypt.
The point, though, is these texts were doomed when there ceased to be a scribal community that cared about them being copied. If you suppressed the heretics in antiquity, you suppressed the transmission of heretical texts except to the extent those texts were quoted in refutations that scribal communities did care about preserving. Actual destruction of manuscripts was unnecessary at that point, although it still sometimes happened like with the works of Arius and Nestorius. At least with Constantine's condemnation of Arius, it seemed to be more of a damnatio memoriae than an a practical act in furtherance of suppressing heresy.