Insomnia has got me to thinking.
Many states have gone in defiance of federal law to pass medical marijuana laws, and Colorado has now passed a law in favor of recreational. I know the newest one is untested and may not stand. However, states (mostly blue) are willingly going against the feds and decriminalizing drugs. If the feared weapons ban happens, could/would states be willing to defy it by either not enforcing the ban or decriminalizing the possession of banned firearms? Not enforcing immigration laws is another example.
"Why yes sir officer I do have a prescription for this rifle."
I know it wouldn't stop federal law enforcement from arresting you, but most contact low key individuals have with the law is local and state. New firearms would likely still be off the table, but all those preexisting ones that we don't have anymore

would still be out there.