No, the entire "Gang of Fourteen" defines "extraordinary circumstances", though ultimately the decision to filibuster based on "extraordinary circumstances" would be sold one way or the other by the Democrats' allies in the dying, socialist "mainstream" newsrooms, which now have considerably less inflience than they once had.
But WE conservatives would have Bush's back, and WE are formidable, to say the least. I maintain that there would be no filibuster but that even IF five of the seven Democrat members of the "GoF" were pressured to bail on "the deal", the Republicans would ultimately prevail in the attempt to "go nuclear" in response.
And if they're not of one mind, who wins? Or does the gang fall apart like the Molotov-von Ribbentrop Pact? I'm afraid you're more of an optimist than I am. I would like to think you're right . . . but I don't.