Yea, I figured both Glenn and Maggie were safe to make it out of S2 alive, because they wern't a happy enough couple yet, but, I think that invulnernability is gone now. Still, I think Glenn serves a role in the show that there's no one to replace him with, so, I don't see him dying just yet, but, I could see TPB ripping Glenn's heart out by killing Maggie (Though I certainly don't want to see that).
I hope that does not happen, only because as a plot point, its too similar to Lori dying and the effect it has on Rick. Rick & Glenn deeply love Lori and Maggie, respectively, so the only sensible response is Glenn taking the same dive into depression and anger. The series does not need more that so soon after Lori's death, piled on top of Rick still dealing with his pain / drepression.
Truth be told, other then the Governor (I do think he's toast very soon) and Andrea (I think she'll live to either take over Woodbury or rejoin our group) there really isn't anyone main I want to lose. I would certainly trade killing Milton in order to keep another regular. Merle deserve to die, but, he's good for the show for drama, I believe.
Milton's death is not a trade-off for the producers, as he's not one of the "heroes," or a genuine, new member (as Herschel's family quickly became in S2). He's being set up as the toadie sitting on the fence, so no matter which direction he turns, he will likely pay the ultimate price in the near future.
TWD's producers love shock and tragedy, so as much as I do not want to see it, Beth, Carol and Judith seem to be walking around with targets on their backs. Hopefully, that theory is shattered by the last 3 episodes of the season.