Of course, Jon Snow's return is bound in secrecy, but given that actor Kit Harington was snapped on set, he's all but certain to return, even if, as he claimed in March, he ultimately appears only in various scenes as a dead body. The full season-six trailer doesn't tell us much more; Melisandre refers to her visions as "a lie," and the final shot clearly shows Davos standing over the corpse of Jon Snow (along with that of his faithful direwolf, Ghost -- poor Ghost!)
But assuming mopey Melisandre can work her magic, one line of speculation has it that, freed of his Night's Watch oath by the technicality of death ("Night gathers, and now my watch begins. It shall not end until my death..."), Ned Stark's alleged bastard (but yeah, R + L = J, am I right?) will be free to look south to the friends and family he left behind. Will a resurrected Jon Snow return to Winterfell? It's possible!