As Lauren Cohan puts it here
Some huge lives are going to be thrown into question.
That's very ambiguously worded, but I think the implication is someone important is going to die in the mid-season finale (unless she just meant the whole Glenn/Maggie capture thing).
I think it's pretty possible that Oscar could die simply because they're raiding a heavily armed compound so somebody
is probably going to die and the guys who aren't in the opening credits are most at risk. The other non-contractual members of the group - Axel, Beth, Hershel, Carol and Judith - are all sitting this raid out.
Of course contracts don't make you invulnerable, as with Lori earlier this season (while getting out of the show was the reason Shane and Dale were offered) so the series could kill someone improtant to go out with a bang. I'd hope whoever they go for it isn't Maggie, Glenn or Daryl, in that order.