Yeah I wondered about fawkeses absence too. You'd think that at least all the noise and racket from the battle would have brought Fawkes out. And the magical barrier wouldn't have stopped him either because fawkes can appear and disappear at will within Hogwarts, he did it once right after Arthur Weasley was bit by the snake OotP.

But I thought that DD would have at least come back with a smart aleckremark before his murderer did him in. I thought, just for a moment, that we would get to hear DDs reason for trusting Snape so implicitly and willingly. I guess DD always needed to believe the best of people and after his extraordinarily long life his careless trust in people finally got the better of him and killed him.