Mid-Season Finale tonight. Look forward to it.
I think, by and large, the main cast is safe. We may lose all of the "red shirts"/Woodbury survivors at the prison but I cannot think of a main character who will be killed off. Forced to pick one I might go with Sasha (debatable if we want to call her a main character, however.) Certainly safe is Rick, Carl, Judith, Daryl, Glenn and Maggie; Beth. Hershel and Michonne are "maybes" but I think will be okay. Tyrese I can see going either way.
But I do think The Governor will fall as the conflict at the prison goes south and maybe as the conflict draws in more Walkers, the Woodbury 2.0 survivors realize what they're being pulled into or maybe Not!Maggie will realize what kind of person The Governor really is and turn on him.
I also think the prison will fall and the episode will end with our cast back on the run off to parts unknown until February.