So anyone who has played episode 2 knows Carver has brought the group back with him. Clearly none of them like him or want to be with him, which could spark a fight. The end of the preview also seems to hint at some kind of fight, whether it be between people or between people and zombies.
My theory is in episode 3 a large fight of some kind will break out and not many people will survive. Nick and Alvin will likely die in an episode or two anyways, based off the fates of past characters, which supports this. That'd be an easy opportunity to kill them both off. The end of the preview seems to hint at some kind of big fight. Last but not least, the episode 4 name and slide seem to hint at the aftermath of a fight. "Amid the ruins" with Clementine seemingly putting on warpaint.
So, episode 3 - there is a huge fight involving Carver's settlement. Episode 4 - the survivors have trouble continuing to survive with wounded people and a shortage on supplies. Episode 5 - nearly everyone is dead, if not everyone. Que depressing episode of Clementine being depressed and wandering through the snow with only hopes of salvation driving her.
And that's my theory. What do you think? Leaving an opinion would be preferred over just downvoting and leaving. :D