Oh, I watched his theories, man! So, this was, basically, just a refresher. It's kinda why I'm so skeptical to begin with. However, here's the thing with this theory; if the Beldam originally fell down the hole, then all Coraline did was toss the key back down to her with her mangled needle-hand in tow.
So, now she has her way out & it's possible that she could think of another way to capture Coraline. I imagine that her death wouldn't be immediate, but really rather long & painful. Like starvation. As such, I wouldn't be surprised if the Beldam became more desperate than ever to accomplish her goal.
Like I said, we don't actually physically see her expire, so there's no guarantee that she IS dead yet. Just because Theorizer says so, doesn't mean it's true.