Snape could well be a goody, dumbledore had to have a good reason to trust him, also the 'I told you so' element is so strong, making Dumbledore wrong and everyone else right - this seems out of charecter with her writing & the wise old headmaster.
What if......?
(I seem to remember harry was not the first infant he attacked),
What if at this time, Voldemort killed one of Snapes young relatives, possibly a son no one knew about if this is the case that would give Dumbledore good reason to trust him. (who would the mother be)
If this the last Book, Harry has to die, then the story can end - or become a spin off mini series on Sky One
If he does not return to Hogwarts, where will the central location be and will we see a bunch of new wizards.
can't wait
p