In the UK he probably would have done, the gun most likely would have been seized and destroyed.
And thereby hangs the problem, some people can be incredibly convincing liars and have no respect for the law and as you say a piece of paper isn't going to stop them doing something. Breaking a restraining order is contempt of court, a serious offence which carries a range of stiff penalties. But the person breaking the order has to be caught doing so first, by which time it could be too late for the victim.