We haven't lost a major character yet this whole season. Who's it going to be?
Well it's easy to point at the people beyond the wall, but let's think about others...
Littlefinger then seems the most likely (Arya has her eyes on him)
Grey Worm (Had his love scene moment and is stuck at Casterly Rock)
Bronn (Cersei wants him punished)
Varys (seems he will die in Westeros as per Melisandre)
Cersei (I still think Jamie will kill her, but maybe not this season like I had thought)