I think there's one word that's very important, and that most here seem to have unconsciously forgotten.
Rhonda's reading: You will destroy that which is undead.
Not kill. Destroy.
I personally think that Rose is going to plunge into the world of the dead to bring Dimitri's soul back. And since Rhonda said "destroy," I think she's going to accidentally mess things up and slam the door between the worlds, meaning that the connection that Strigoi have with their lost souls will sever, destroying them all. Because seriously, doesn't that seem like Rose: intending to do one small thing and accidentally changing history by destroying all of the Strigoi- forever?
Chipping in on the tarot cards, it always seemed obvious to me that the upside-down sun stood for 'undead'. The sun is life. An upside-down sun doesn't stand for death, but the opposite of life- undead. Of course, I'm not a tarot card reader, but that's the way it played out in my mind.