From the Oxford English Dictionary (online), under "vestige"

b. A surviving memorial or trace of some condition, quality, practice, etc., serving as an
indication of its former existence. Usually in plural.

c. Without of, in preceding senses.

From the Oxford English Dictionary (online), under "scripture"

a. The sacred writings of the Old or New Testament, or (more usually) of both together; Holy Writ; the Bible. Often with holy prefixed.

c. Something as surely true as Holy Scripture; = GOSPEL n. 4.

d. sing. or pl. Sacred writings or records.

e. fig. and allusively.

Thus a "vestige" of "scripture(s)" could indicate at least the following phenomena:

(1) Some surviving trace (footprint) of material that is/was associated in some way with "scripture" as we have come to think of such writings in relation to "canon," but not necessarily dependent on or derivitave of canonical "scripture" -- this would encompass the current sense(s) of "parabiblical," "rewritten bible," and the like, but also avoid the explicitly canonical connotations by envisioning particular "scriptures" as authoritative, but not necessarily defined by being part of an exclusive/closed collection (canon) of what came to be "Scripture";

(2) Some surviving trace of material that was once considered to be "scripture/scriptural" as an earlier community (or witness) thought of that category (authoritative relative to the situation), without necessarily being related in content to what came to be "scripture" in a canonical sense -- e.g. was the "Community Rule" from the DSS "scriptural" for some community?