It is important to keep in mind, that not everything that is unconstitutional may be remedied by the Judiciary. You can get into a lengthy scholarly debate with respect to the constitutionality of the so-called "Slaughter Rule", but weighing the deference that the Judiciary has historically given to the Congress on enrolled bills, it's unlikely that they'll address any constitutional infirmity on the process of passing the legislation.
Mark Levin isn't a stupid guy, and I suspect that personally (if yet not publicly acknowledged), he knows the very same thing. The Court is unlikely to find the problem justiciable.
If it passes, Constitutional challenges will need to be brought on the substance, and not the process.
He’s already acknowledged that the ball will be in their court. They determine whether it is in their realm or not.