It was my understanding that the imprint left with Endurance was to be carried to its resting place inside Requiem, where the Chief (and later, Halsey) encounters her. I don't believe the imprint was meant to be used as a mutation seed, as in the case of the Ur-Didact and Iso-Didact, since Endurance was slated to be the last of the Didact's Prometheans to be converted into a Knight.

I also read that contact with Chant-to-Green more as a transfer of title and authority than an imprint of herself and that the Librarian had resigned herself to "going down with the ship," so to speak, and dying with the species she treasured so much.

Interesting (but related) observation: I think it's also entirely possible that there are still other living Forerunners (i.e. Chant-to-Green, IsoDidact, etc.) still in hiding somewhere, unless I misunderstood something about the way Silentium ended.