Earlier today, JK Rowling hosted a live web chat on Bloomsbury's official website where she answered several questions about Deathly Hallows:
Michael: Why didnt fawkes come back to help harry I would have thought that since harry was so loyal to dumbledore, fawkes would have been harrys new pet
J.K. Rowling: Something had to leave the school for good when Dumbledore died, and I decided that would be Fawkes. Dumbledore was a very great and irreplacable man, and the loss of Fawkes (and the fact that he was 'non-transferable'!) expresses this symbolically
Read the entire transcript at the link below! Thank you to everyone who sent it in.