Without a doubt you are correct. Will Snowe and Collins follow soon??
I have seen one party rule and it is not a pretty thing. In fact, it is likely the end of democracy or of the republic if you prefer.
Probably not unless they face a serious challenge in their respective primaries. I'm not sure when they're do fro reelection, but I don't believe either has to stand for reelection in 2010.
They'll continue to have more "power" as deal makers or breakers, even if the Dems have 60. With Ben Nelson and a couple other more moderate Dems in the Senate, I don't believe a filibuster-proof majority will hold for every issue. JMHO.
Given how liberal their state is, they are unlikely to get any serious (or even slightly serious) primary challenges. So, no, they probably won't switch.