User blog comment:Rena the Boss/Miniview - 5.04 - "The Broken Kingdom"/@comment-27031632-20151019172201/@comment-27075962-20151019192035

As for the key, it was needed to resurrect the Dark One, I'm guessing. The whole "life for a life" thing. This time around, that wasn't the case; they were after the dagger, not the resurrection of a Dark One.