I just lost a good 800 words, so this is going to be shorter than I intended originally.
Anyway: I like the idea of Odin and Uriel trading people like baseball cards. And I personally believe the loophole is going to be Ragnarok; every source for that part of the mythology I've found specifies that Odin leads the Aesir and all of the Einherjaren into battle against Fenrir, which would presumably include Murphy.
And the whole "I'm here but can't stay" inevitability is probably already going to happen in Mirror, Mirror, presuming Murphy doesn't hate Dresden in that timeline. That's where I assume Harry will find his catharsis. Maybe with some other lost characters, too.
On Ragnarok: I don't know where Jim intends to source his interpretations. It could be the Poetic Edda or the Prose Edda, but Snorri did a LOT of editorializing in the 13th century, and directly contradicts a bunch of stuff from the original, surviving Old Norse texts. He really seemed to want to impose a kind of order to Norse mythology that didn't really exist in what you'd consider their canon. For example, Snorri directly states that those who die in battle go to Valhalla, while those who die of disease, accidents, or old age are sent to Helheim, which is a clear-cut rule that is nowhere to be found in the older material. The closest thing to that kind of rule is that Odin and his Valkyries will "choose" from among those who've died in a conflict, but it's not really clear what criteria they use, and it doesn't stipulate what happens to those who weren't chosen to be an Einherjar.
Anyway, I'm looking forward to seeing Jim's interpretation of Loki. The real one from mythology, not the bastardization we have in these Marvel movies, however entertaining Tom Hiddleston might be. I wonder if he's currently sleeping under Demonreach. Are there snakes there?