Section (C), belowAnd someone would have to go through the law, but many bans like this allow selling off EXISTING inventory.
The provisions of this Section do not apply to the
manufacture, delivery, sale, import, purchase, or possession
of an assault weapon, assault weapon attachment, .50 caliber
rifle, or .50 caliber cartridge or causing the manufacture,
delivery, sale, importation, purchase, or possession of those
items:
(A) for sale or transfer to persons authorized under
subdivisions (1) through (7) of this subsection (e) to
possess those items;
(B) for sale or transfer to the United States or any
department or agency thereof; or
(C) for sale or transfer in another state or for
export.
The way I read an FFL could even continue to buy new inventory, provided it is intended for sale out of state (or for sale to exempted parties like law enforcement)