I think it has to be one of the four people held captive in that van. They kept showing that first person point of view from someone in the van where it is dark and just a little light is coming through some bullet holes and the crack where the doors open. That is likely symbolic of the first person view we get at the end when their head is being bashed in by Negan. Whoever's viewpoint we are seeing in that van is my guess for who gets killed. So that leaves Rosita, Glenn, Daryll, and Michonne. Probably either Darryl or Glenn.