As much as it breaks my heart to say it,I don't think they are commin' back(Sirius,Albus).I kept my hopes up in book five for the same reason,Sirius was one of my favorite characters and I just could not believe he was gone.I understood things the way I wanted to.I thought to myself "he fell through the veill but it did not say he died and then fell through the veill,so he might still make a comeback in book six.But instead of that I faced a new tragedy,another of my favorite characters died.That's when I thought "hmmm.....I'm strating to suspect Sirius is not commin' back".Of my favorite characters,there still remains the twins(god I don't know how I could do without their,ummm......"sens of humor" to say it one way) and one of the least liked characters,Severus Snape(he is such a complex character,he hated Harry's father but still he keeps saving Harry's life whenever he can for starters).Hmmm......only thing I can think of to keep my hopes up is that Dumbledore was closely related to the Phoenix(his Patronum was a Phoenix,his pet was a Phoenix and at the end a curtain of white smoke came out of his tomb in the form of......yup you guessed it,a Phoenix).I truely wish for him to come back,but honestly I don't think he will be back.Just like the case of Luke Skywalker being the one destined to defeat Darth Vader,not the legendary
Obi-Wan-Kenobi(who died) nor the all knowing,wise and powerfull master Yoda(who also died).But let us wait and see.