Basically, the Dems have 59 votes. They need 60 to pass something.
If, say the Baucus plan (as crappy as it is) becomes the Plan, and Snowe jumps on board. Boom. It passes with 60 votes. End of story.
But let's say Snowe holds back (more than likely because she doesn't want to be the only GOP Yes Vote for Reform), all of the sudden, Health Care Reform has 59 votes...or fewer. Does that mean Health Care Reform dies?
No.
Not only does it not die...it gets better.