The way that Hitler was defeated was that Berlin was pounded into rubble that put paid to the revival of stab-in-the-back theories that followed WW1. Japan was defeated by two nuclear bombs that replaced any hope of resistance with fear of obliteration. Bin Laden killed in his pajamas, and his body was dumped in the ocean: an ignominious end to a man who claimed to take divine inspiration for his acts. The supporters of these ideologies had to experience the shame of total defeat, and see no hope, before they moved on.
A hard Brexit, while causing some pain for the British public, may well be the medicine needed to show its most fanatical supporters the error of their ways. Otherwise their resentment will fester for decades longer.