The Dems may be falling into a no-win situation, actually. If they have 41 votes or greater against Alito, many people on the left will demand they filibuster, then Frist will respond with the nuke. They may wish to save the filibuster for a next time (it can only work if they have the popular support of the American people, I believe).
But honestly, if there really were extraordinary circumstances to filibuster Alito or some other nominee, it wouldn't be necessary because that person wouldn't be able to get majority support on the floor.