Each Senate establishes its rules at the beginning of the term. A simple majority makes the rules. If 51 Senators say no Filibuster for this particular Senate session then this rule governs the 111th Senate.
It really is that easy. So simple. Very very easy. Sometimes in life the solutions are simple. In 1975 a mere majority reduced the number needed to filibuster from 67 to 60.
Just abolish the filibuster by majority vote. Then you don't have to worry about Joe Lieberman or 60 Senators. Democrats have the majority, use it. This is one of those times. If we govern well we will stay the majority.