The essential point of the post was that we were due for death of a mentor figure. Yes, that's normally the Hero's Journey archetype, but not necessarily. Focusing on the conventional interpretation to dismiss, instead of addressing the point, is the fallacy known as "logic chopping."
Your point read to me as "the Hero's Journey calls for the death of the mentor, and Murphy is the Mentor, so Murphy was due to die." I'm fine saying that's a misreading of your argument. So my response wasn't irrelevant to what it appeared you were saying.
You hid a lot of your point in the word "structure" and relied on Murphy being a mentor. I'm not sure what you mean by structure. Murphy is a mentor under the Hero's Journey, but so is Harry's ruby with knowledge of the ways. I don't think Murphy is Harry's mentor outside the context of the Hero's Journey. That's a stretch of the plain meaning of the word. Confidant, advisor, and critic are all better descriptions of Murphy's relationship to Harry. Sure, she has more investigative and martial arts experience than Harry, but teaching those things to Harry has never been the core of their relationship or the purpose of her character.
If your point is that it's time for Harry to stand on his own, I'm not so sure he's ever going to do that. He might be more isolated in his personal life having lost his best friend, but I don't think he's going to be much more isolated when he's in the field doing things. Currently he's always going around with the Alphas. I think it's likely that he's going to have a sidekick or crew in every book. Harry hasn't been on his own since
Storm Front.
If we're due for the death of a mentor,
i.e., someone the
apprentice relies on for their experience, expertise, and help in a certain field that the apprentice is also engaged in, Murphy doesn't fit the bill. Ebeenezer, Rashid, Mab, and Bob fit that description much better. One reason that authors kill off mentor figures so often is that the mentor should be able to deal with whatever challenge the main character has to face with ease. That's never really been the case for Harry. He's never been able to call someone up and ask them to solve his problems for him. No one has held his hand and walked him through his adventure. He
may have been able to ask Eb, but he's never done it. He's asked him for help a time or two, and Eb has volunteered his help a time or two. In the death of the mentor trope (which has little to do with structure), Eb is the mentor, not Murphy.
Now, it might be time, structurally, for the stakes to be raised so we don't feel any character (other than Harry) is safe. But that's completely different than "death of the mentor."
If it is time for the Hero to leave behind the Mentor, Harry being kicked out of the White Council and Butters having Bob could accomplish that. Except for the part where Harry just borrows Bob whenever he needs to figure something out.
And no, Death of the Mentor, isn't part of the Hero's Journey. The mentor is just someone or thing that helps the hero accept the call to adventure. The call to adventure has Harry on speed dial and he always answers on the first ring. Also, Campbell described this as "supernatural aid" and the closest by the book example from the Dresden Files is when Rashid gives Harry the anti-faye glamour ointment and piece of the stone table in SK. Death of the Mentor comes in when you have a figure like Gandalf or Obi-won who is just leagues ahead of everyone, so the hero is just going to defer to him and/or rely on him. A good example of that from the DF would be when Harry died if we were following Butters or Murphy instead of Harry.