I think it will be either Mashonne or Abraham. Here are my reasons.
Mashonne - Rick isn't supposed to have a love interest that last very long.
Abraham - Main character, but expendable. Some would say his fighting ability makes him irreplaceable, but I disagree. I think he makes poor decisions that could get someone killed.
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Sleeper: Coral, that is hurting Rick the most and that is what I think Negan wants to do.
Probably not Maggie: Some will say no way, because killing her (a pregnant woman) would be going too far, but they did kill the little girl (watch the flowers). Also, unless she miscarries, do we really want 2 kids to cart around the apocalypse?
Not Daryl: Too much of a fan favorite, but if it is, I think it will hurt just as much, if not more, than Rick.
The favorite: Is probably Glenn and I wouldn't be surprised, but I think he is just as much of a fan favorite as Daryl.