Fawkes' Absence after Dumbledore's death

[strange_familiarities]

No: HPFGUIDX 178980

I have a question about Fawkes. Does he have some sort of mortal bond
with Dumbledore? He seemed to have totally disappeared from the books.
I might have missed something, but I do not understand where he
disappeared to. Also, if he did not die, then why didn't he rescue
Snape? In CoS, Dumbledore explained to Harry that Fawkes helps those
who are loyal to Dumbledore, and who was more loyal to Dumbledore than
Snape?