I'm being utterly foolish and hoping that since JKR has basically milked pretty much every other myth for what it's worth, the fact that Fawkes "left" means that Dumbledore will return in some way. He reminds me of my Opa. I knew he was going to die, but still....

Snape... I personally think, like you, that Snape and Albus had a Plan. It might not have played out exactly how they wanted, and maybe Snape had to improvise, but I'm willing to not turn my back on Snape yet.