So Jon's coming back?
To add to this, there's a couple things that make me think he is (outside of what's been mentioned).
First, if Martin wanted him dead I'd think he would have him cut down with something more than a couple stabs from a knife or two. Why do that when you could take him down with a sword instead and leave no doubt.
My newest crackpot theory to that is Melisandre has now realized that Jon is Azor Ahai reborn and she had it done so that he could be reborn.
Second, his arc hasn't finished yet. By a long shot. Just too many unanswered questions. He is also able to warg and others have warged into their animals to save their souls so to speak.
Lastly, Martin did an interview awhile back and when something was said about Jon being dead he said, "So you think he's dead ah?" in a manner that suggests that he's still alive in some shape or form. Especially since Martin has had a history of setting wayward fans right on theories and etc.