I don’t think the SC will rule against an individual right. But if they do the ruling will accomplish nothing.
States that don’t like this ruling and want their citizens to be armed will simply declare all able-bodied citizens over 18 to be members of the militia. That’ll probably be the overwhelming majority of states. Certainly all of the South and most of the West. The anti-gun left wouldn’t be able to do anything about this because the SC just ruled the 2nd Amendment is a collective state right and this is how the states choose to exercise that right. So the actual result of such a ruling will be that the liberal cities in conservative states would have their anti-gun legislation overturned as a result of this action. Bring it on!!
Any ruling by the Supreme Court that the Second Amendment is a "collective right" will have no impact in most of the US, since that is the mistaken ruling that most Circuits have used since 1939.
There would be no need for any state to take any action. If such a state has its own constitutional protection of an individual right, lack of a federal protection in no way reduces that protection.
Like the medical marijuana case, the situation with the right to keep and bear arms, is that the federal government has routinely violated the rights of citizens in the various states with bans, regulations, and taxes. It's far past time for this to stop.