I don't really know how the Aveda Kedavra curse works...
Groo, I do think Harry will, by the end of the seventh book, have the power to perform the curse.
And with the deal about Harry not wanting to cause pain, I think what happened in OotP with Bellatrix could have been, like, a white-hot rage that would simmer down... but after two more years and a lot more losses, I think he could have the kind of festering anger that would be needed to perform the curse.
About how Voldy took precautions to not die, even when his own Aveda Kedavra curse rebounded on him, remember, he's vulnerable now. He settled for mortality right now, with the intention of becoming immortal again sometime in the future. When he used his father's bone, Wormtail's flesh and Harry's blood to get a body again, he made himself vulnerable to death, and as far as we know, he hasn't done anything yet to change that.
That said, I am actually leaning more towards the theory that it won't be AK that will kill him. No idea what will, but I do know there are other ways for wizards, even great ones, to die.
So... we'll see.
