Let's try to analyze the chances by character:
Cheri and Morris:Cheri was an enigmatic character, pretty interesting since she had a secret past, but I think that she and Morris were only created for showing some secondary interactions between John and other teenagers (with a normal life, in case of Morris, and not that normal in case of Cheri, which made the interaction a little more interesting).
Given the writers strike, all the plans the writers had to develop that teenager interaction changed, and the writers decided to simply turn the page and forget about them. After all, I think that was a secondary plotline with the [presumably] sole purpose of describing how John gets in trouble for having some friends/relations.
So, not a big possibility to develop those characters, at least, not far beyond that.
NEVERTHELESS, Cheri could be the troubled daughter of a deputy, couldn't she?
Chola:Weird character indeed. Pretty interesting too.
Remember that, despite she never said a word, she had the key role of knowing where the false Sarkissian was hidden (I guess she wrote that in a piece of paper
) and also there was that curious interaction with Cameron (she taught Cam all that make-up stuff, you know, that was an important contribution
).
Anyway, I can't see how could Chola have a place in all this. Unless she got across Cameron, got curious, followed her, and ended up helping Cameron in some difficult situation. But I'm just letting my imagination fly. I shouldn't. Not even likely to happen. That would be pointless.
Terissa (or even Danny) Dyson (Should have been included in the poll, sorry 
):Before reading Tonya's post I would have said: "Hey! They had suffered enough. Let's leave them alone..."
But now, considering that post, I still think there's no more room for Terissa but having a grown up Danny would be an interesting development of the facts
Doctor Silberman:This character has grown a lot due to the GREAT performance of the actor. That would be totally exciting for me to see some more interaction between Silberman and Sarah.
I also can imagine Sarah being locked up again in Pescadero, having deep talks with Silverman (even they might turn up being friends after all) and then being rescued by John at the beginning of the third season!
CarterToo short to be Cromartie, but also too freaking creepy for not being a good choice ;D
I don't think he/it can turn the switch on his/its own ("he" or "it" is your choice) and start hunting John, since it seems like he/it was programmed with only one mission (get the Coltan and wait for new instructions in stand-by mode) but certainly there is a good chance that we can see Carter again. How?
Well, I think that, since Catherine Weaver is making preparations for Skynet to succeed (is she/it?), it seems probable that she already knows about the bunker and the Coltan. So, Weaver might find that terminator and reprogram him to protect John Henry/ find the Connors
Conclusions:All that said, I couldn't vote for just one of them.
I voted for Silberman, though. But I would also dare to say that Cheri, as the possible daughter of a deputy, and Carter, as the reprogrammed terminator, and even a grown up Danny Dyson, have their chances to come back
) and also there was that curious interaction with Cameron (she taught Cam all that make-up stuff, you know, that was an important contribution 
):
