True. Congress passed the Respect for Marriage Act , which created a federal law which explicitly legalizes same-sex marriage.
So even if the Supreme Court were to reverse the case on same-sex marriage, the fact that you now have a federal law which explicitly allows it fundamentally changes the legal landscape surrounding same-sex marriage.
Reversing the Supreme Court decision would legally say that there is no constitutional right to same-sex marriage, but such a ruling would not over rule the Federal Respect for Marriage Act.
Exactly. It was enacted in response to a possible future reversal of Obergefell.