They've planted WAY too many hints that "as long as Dumbledore is around, Harry is safe."
When you see the way he toys with Voldemort in Phoenix, you know there will NEVER be any tension in the books. Albus shows up, and the fight is over lickety split.
In addition, the standard "drama" style mandates it. We need to hit bottom in book six, so that Harry, the Hero, can have a dramatic comeback in book seven.
If you think about it, Minerva has absolutely no function in the books... except to be the next Headmaster (err... Headmistress. But when I write that, I see Maggie Smith in black leather, and I'm made most uncomfortable by that image!)
Oh... and I'm also thinking that in book seven, Sirius comes back from the "other side". This will be Harry's "reward" for his victory. Without it, the ending would be most hollow.
Oh... Hagrid is the Halfblood Prince. He's half giant, and the giants are playing a much greater role (as we see by his mission in Phoenix, and his return with Grop.)
Now, we can check ALL these things on Saturday... I've got three copies pre-ordered for midnight pickup, as three of us in the house are refusing to share!
Anthony
You can lead a horse to water but you can't make him think.