The death of Viserion may be what finally destroys the Wall and allows the White Walkers to usher their wights into the Seven Kingdoms to spread death, destruction, and the terrible cold.
Well, the White Walkers never had a dragon before, and we’ve seen what one of Dany’s dragons is able to accomplish.
The great Wall may be a feat of architecture that has stood for countless generations, but it’s also made of ice, and a dragon could definitely bring it down.
She roasted the majority of the Lannister army without so much as breaking a sweat, and she did some serious damage to the wight army in “Beyond the Wall” until Viserion was killed.