The Supreme court has no say in how the House or the Senate conducts their respective business.
They did when we impeached Clinton, and recounts in Florida. They have been involved in other Constitutional crisis'. If Republicans try the nuclear option the rats will claim it is illegal, and send lawyers to the SCOTUS. Bank on it.
IMO the SCOTUS would side with the rats based upon a long history of previous Senates abiding by the rules of the last Senate.