I think it's going to take me a few days to digest what I've read - both the book and what you wrote here. I only finished the book last night. I'm not convinced Dumbledore is really dead. Your idea of whether there is a good equivalent of a Horcrux is interesting.

And yes, you have managed to convince me that perhaps Snape really isn't evil. Maybe he and Dumbledore planned the Avada Kedavara scene all along - maybe it wasn't real some how. There were flames at Dumbledore's funeral - yes, maybe he will rise again like Fawkes can.