...would the GOP even use a filibuster if it could?
In the past there is always some “gang of (fill in number here)” that put the screws to it, lead by Republicans (usually McCain).
I think there are a few things (probably very few) that would galvanize them....card check for instance. Of course, Collins and Snowe could just cave and it would be a moot issue whether Chambliss is there or not.