Board Thread:General Discussion/@comment-179.212.90.245-20151018194404/@comment-6881629-20151018205711

The crest is gone when you complete the quest you basically swap it for the other item and i'm pretty sure the forge will only work once (theres a technical explanation on the thread here), the quest can be pretty buggy i wouldn't risk leaving the area before using the forge especially if your on a console (if you do make sure to keep a save to go back to).

Being a qust item i doubt you could drop the crest though.