if all guns were banned tomorrow....
people would figure out how to make fireworks, cannons, flamethrowers, and basic sharp explode-y things to protect their home.
come to think of it, if my house security system video shows bad guys in my living room, it'd be cool to activate some kinda cool bleach explosive mist to blind/poison them. Safer than a gunfight anyway haha.
People can print gun stocks using 3D printers, and for the most part, 3D printers are still completely unnecessary, overpriced things with not enough uses. If guns were suddenly banned, then 3D printer technology would skyrocket, as would homemade gun kits. It woudn't be as nice as a glock or AR-15, but could send hot metal at a perp as needed.
OR everyone would just join the police so they could pack heat.