The SCOTUS decision does not void the entire law, only the law as it applies to gay marriages.
Your (and others') interpretation that it voids the entire existing law is incorrect.
And what law school did you flunk out of?
The Supreme Court does not have a line item veto.
Do you recall how it was noted that Congress forgot to put a "saving clause" in Obamacare? It was noted that their failure to do so would mean that if ANY PART of Obamacare were found to be unconstitutional, then the whole law would be unconstitutional and void? That is why Roberts was so adamant about finding any way to save it.
Well, the same is true of marriage laws. When a law is passed by the legislature that includes some provision that is found to be unconstitutional, the entire statute that contains the governor's signature is voided and the legislature then needs to rewrite the law and get it passed. If there was another previous statute that was overturned or amended when the unconstitutional law was passed, then that statute goes back into effect.
The Supreme Court voided every state statute that contains the words "Marriage shall be limited to one man and one woman". So those states that have those words are currently operating either under a previous law that did not contain those provisions or they are operating without any marriage laws whatsoever.
And if people can still get marriage licenses without the limitation of "between one man and one woman", then if the State is going to recognize marriages and issue licenses, then it is not merely gay people who can get married, but polygamy is now the law of the land without limitation. Two men and three women? Five women and three men?
Where is the limitation?