I've read posts suggesting the Individual States (for John Roberts clarity) should just nullify the USSC decision. However, you actually bring up a legal issue that is problematic to States' laws and constitutions, providing such stipulate that marriage is between and man and woman. It will be interesting to see how the States handle this.
Most State Statutes do not include language that if one sentence of a statute is declared unconstitutional that the remainder of the statute will remain in effect.
When these laws limiting marriage licenses to one man and one woman, not members of the immediate family or first cousins, not under the age of 17... etc., were enacted, nobody in their wildest dreams ever thought that even one sentence would be found to be unconstitutional.
But since the Supreme Court has ruled that any marriage law that prohibits same sex marriage is now unconstitutional, the entire marriage law has been declared to be unconstitutional and the state is left with no law at all on the books governing marriage.
Unless the State Legislatures pass new laws redefining the terms under which a couple or group of people may get married, then there is no legal authority for the issuance of marriage licenses or certificates.
Any County Clerk who issues a marriage license to anyone (gay, straight, whatever) is doing so without any legal authorization to do so.
The Supreme Court not only legitimized gay marriage, but ended marriage for everyone at the same time.
SCOTUS ruling is NOT CONSTITUTIONAL.
Everyone who has sworn an oath to uphold the Constitution has an obligation to ignore this ruling and to declare it illegitimate.
States can continue to abide by their state law and refuse to issue marriage licenses to same sex couples, or they can refuse to give marriage licenses to anyone. They have no legal authority to do anything else.