It’ll be appealed and overturned.
It will be ignored.
Meanwhile the decision should be duly ignored.
Maybe, Maybe not.
The only court of appeal is the Supreme Court, as this is a First Circuit decision.
The plaintiffs could ask for an en banc ruling, I suppose.
The Supreme Court has been refusing to hear cases that uphold the Second Amendment for about three years.
If the case is not heard en banc, and the Supreme Court refuses to grant Ceriortari (to hear the case), the case will stand in the First Circuit.