I think Glen is going to bite the dust.
I think big abe and eugene were other possibilities, it has to be someone with enough 'impact' to warrant the wait and also make negan seem like he means business.
I don't think it's abraham precisely because he kinda kneeled upwards to send a signal to negan that he was willing to take the hit for the team despite his new found passion for existing with Sasha. Negan don't strike me as the type of guy to bash someone's brains in because they are a willing sacrifice, also abraham is more useful to him alive than dead right now.
Eugene, I could see him rigging the rv to explode or something so he seems even more valiant than he has steadily been built up to be.
Glen well all the obvious hints were there, he's going to be a father maybe so will make it very emotional and also good character arc for maggie. Obv it's in the comic and it was also kinda foreshadowed at terminus infront of the bloody steel trough, he was gonna get whacked by a baseball bat next but gareth came in asking for bullet counts and feral grimes took care of them first.
Daryl is way too much of a money spinner and fan favourite for them to knock him off at this moment imo, he is up there with rick as THE face of the show. He was also injured recently which means he's likely not going to be killed.