FWIW, my money is on Abraham being the one Negan killed. Negan would likely see him as one of the strongest and therefore a threat. From the fans perspective he's important/liked, but not revolt-level important like Darryl/
/Glenn/Maggie. Seems like the obvious choice for the creators - important character, but not central character.
Plus on Talking dead, the creators said a lot changes for the survivors because of the character that dies. Can't be a small character like Aaron or Rosita. Abraham touched a lot of people - Sasha, Rosita, Eugine - and most the others to a varied extent.
The other cliffhanger no ones talking about! I'm very interested in how the "Knights" will play into all this. I've not read, nor do I intend to read the comics - and don't know if the TV version would follow anyway. For that reason, I'm really not even interested in the comics version. I hope they will be a "good" group like it was suggested - as they offerred to help Morgan and Carol. Maybe they form an alliance with Rick's group and Hilltop to take on Negan. By the looks of things, Ricks gonna need a lot more soldiers!