It could be Eugene (Josh McDermitt), who might have switched his allegiance from Alexandria to the Sanctuary, unbeknownst to his friends who might be trying to rescue him. If anyone from Alexandria tries to include him in their plans, he might snitch.
Or it could be Sashita, a.k.a. Sasha (Sonequa Martin-Green) and Rosita (Christian Serratos), who are on an extracurricular suicide mission to take out Negan, and there's no way that's going to turn out well. They're probably going to get captured -- or worse.
Chances are, we'll be saying "good-bye" to one of these characters by the season finale.