As the truce winds down, Hamas faced two options: rev the war back up, or bide their time. Long-term, time is in their favor--Arab Muslims are outbreeding Jews by quite a bit (although they're still quite the minority). But it's very long-term. So Hamas is going with option 1.
First: rocket attacks have increased significantly. Because Hamas has no credible control over the people of Gaza, the only reputation blow it takes is for letting these rockets go is on its administrative and security abilities--a reputation it doesn't really care about anyway. But Hamas allows doubt to loom over whether it's orchestrating the attacks or not. The rockets are making living near Gaza nigh-untenable for Israelis, even though none have died. But that's the point: it's terror.
Second: Hamas has generally agreed that the cease-fire will end. They claim they will only "respond to Israeli aggression," but the cease-fire gives Israel a lot of leeway to really hammer down on the West Bank for rockets flying into Israel--if Hamas doesn't want large-scale war, it had better hope that it does have control over such rocketeers. The lack of a cease-fire will lift any veil that Hamas is actually trying to keep rockets under control--and Israel has shown that it's unlikely to cow to international pressure. Hamas probably knows it, too.
Israel probably has a plan to make a surgical strike into Hamas if they provoke it. Israel had offered to extend the truce--it was Hamas that declined, even after Israel released a few hundred Palestinian prisoners. Along with the rockets, Hamas is pretty clearly asking for it. Expect the Israelis to have something very precise in their sleeves to unleash on the Hamas leadership if they start acting up after the truce ends. Especially with Livni's declaration that Hamas has to go by force, don't expect Israel to play nice with Hamas, regardless of whether Kadima or Likud takes the polls in January.