Murphy got killed. Butcher uses it for the emotional punch. And then he resurrects her. The whole scene with Rudolph turns out to be about Harry losing his shit because Rudolph made his girlfriend go away. Not because she died, because, well, she didn't.
To be fair, at that point in the story when Harry loses it, he had
no idea Karrin would be Chosen. As far as he knew
in that moment, she was D-E-D, dead. So Harry's Roaring Rampage of Revenge really was about her dying, not just "going away." He (and the readers) don't know better until pretty much the end of the novel. It may change the
perception of the act in retrospect, but not the initial motivation for it... if you catch my drift.
Yeah, I know it's a tiny point to quibble over, but I think the nuance is important. We're supposed to see Harry stumble in a moment of extreme strain, when he's experiencing one of his worst losses in the series so far. He loses love, he loses faith, he loses hope; all that's left is pain and hate, until he gets a wake-up call from Butters' Sword. I think we're meant to take that seriously, as a warning of what Harry could become if he steps off the "path of Good." I
don't think that really changes when we learn things weren't exactly as dire as Harry thought they were at that point.
Does it cheapen death as a threat in the series when Murphy isn't really D-E-D dead? Well... kind of, yes, depending on the reader's perspective. Coming back from the dead isn't unusual in fantasy works. We've seen Harry do it, more or less; we also got enough hints sprinkled through the narrative foreshadowing the concept (Murphy as an avenging angel in Dresden's Sight; her training with the Einherjar; her call sign "Valkyrie") that this wasn't a total shock. I'm kind of neutral on it until I see what Butcher does with this set-up. I have a feeling we're just about out of get-out-of-Death-free cards, this close to the Endgame... and the next heroic deaths are going to hurt that much more because of it. But as always, YMMV.