I think Dumbledore is dead because JKR said it had been planned to come for a while. However, I don't think Harry will go on completely on his own because the other 6 books so far have centered around Harry at Hogwarts with Ron and Hermione, so if Harry was to just go off on his own, out of Hogwarts, then it would be so much different from the rest of the series - I think Ron and Hermione are almost as important as Harry - it wouldn't be the same without them.
As for the whole Snape thing, maybe he did kill Dumbledore reluctantly because of the Unbreakable Vow he made. However, why would he have made this vow in the first place if he really was on the 'good side'. Also, if he truly was good then he would have considered breaking the unbreakable vow and dieing as a result - but saving Dumbledore - a better wizard. I'm not saying he would necessarily have died for Dumbledore but he would have at least been slightly hesistant before killing Dumbledore!
That's just what i think anyway!