Hi Tom,
This is what would make the most sense for how they would handle the 2nd season:
The townspeople figure out a way to lift the Dome. The is brief jubilance. Then, the Dome slams down again, but this time covering a wider swath of area. Some people would have gotten out; others would have gotten in.
This allows for the producers to keep the same setting, introduce a new "mystery," i.e., how to raise the new Dome, and also for some chracters to exit and new characters to be introduced for the new season, allowing for new relationships, conflicts etc for the Second Season.
This prediction probably won't prove true, but if they wanted to keep things from getting too stale, it would be one way to do it.
