I don't think Hershel or Glen is going to die.
Honestly, I would put money on the nobodies dying tonight. The 'nobodies' would be (had to do a bit of Google searching here): Jimmy, Patricia, maybe Beth (one of them gotta survive lol). I doubt they will kill T-Dog because it would seriously be an insult to the actor who was COMPLETELY useless this season and I believe the writers have something big planned for T-Dog when Merle is back in Season 3.
What I think is going to happen is that the zombie horde is going to ambush the farm and they have no choice but to leave the farm, which I hope will lead them to a new location. I've read the graphic novels so I'm expecting them to run into a prison and that'd be the end of the episode.