I like what you're thinking Needle, except wouldn't it make more sense for Jon to blow the horn? I know the Targs think they're gods, but how are they not mortal men/women? Surely Jaime and Khal Drogo proved the opposite. Now Jon on the other hand, assuming he's resurrected by Mel, wouldn't really be a mortal man. So he could blow the horn safely, with Aegon, Dany & Tyrion as the dragon riders.
I'm wondering about Dany at the end though. She thinks earlier that the Targs never get ill, then at the end she's showing all the symptoms of the flux. What are we to make of that? It would be so GRRM to kill off Dany in the next book, and then we're back to Aegon, Tyrion and Jon!