0% chance Jon Snow isn’t alive in some form. Anyone who’s read the books knows that the Stark children all have that weird “warg” ability that allows their consciousness to enter their dire wolf. The fact that the trailer shows all of the Stark children (including Robb) and then shows Bran warging (weird to say that as a verb) means somethings up. It’s about time they brought that detail into the show anyways.
I’m guessing Jon warged before he died, and that Mellisandre can use her dark independent woman powers to put it back into his body.
Aaaaaand I’m also now questioning whether or not the same could’ve been done for Robb, ya know, had his direwolf not been arrowed to death.