I was very surprised this never came up in oral arguments, because it is my recollection that at one point the bill DID contain a severability clause and it was REMOVED before final passage, a strong argument that the lack of a severability clause was not an oversight, but an intentional decision by Congress!
Oral arguments can be rather informal and incomplete. No question that the inclusion, then deliberate removal, of a severability clause WILL be addressed in the final verdict.