He was going to be left to die in an ice cell, or possibly hanged, but Maester Aemon (Targaryen) is having none of this Jon-is-a-Turncloak business, which for some reason is causing problems for Janos Slynt and Alliser Thorne. So they're going to send him to see Mance Rayder instead, to parley. And they want him to murder Mance to prove his innocence, which will get him killed. It's similar logic to drowning witches.
Tormund and Mance are both pretty friendly towards Jon. Even though hundreds of wildlings have been killed there is no hatred towards the Watch, who are deemed to have put up a jolly good fight. In fact the wildlings in general seem like awfully reasonable, rational people. It's questionable which civilisation is the most civilised.
Mance does in fact have the Giant Horn which could supposedly destroy the wall. But Mance isn't too keen to use it because he's not really running towards Westeros so much as away from the Others, and the wall would be pretty handy to be on the other side of. He wants to be let through in return for not blowing it.
Jon is wondering how he's going to murder Mance in front of his heavily pregnant wife when it all becomes moot anyway because Stannis has turned up, and we get a good look at what a well organised army with proper knights and big horses can do against a disorganised mob even though greatly outnumbered. Which mostly seems to be that the disorganised mob runs away. Jon is left being the midwife as Mance's wife is giving birth.
I'm starting to think that Jon might just get away in all the confusion.
And if Stannis is here, I can only assume that Davos has convinced him that bad things are happening beyond the wall and he ought to do something about it.
