They know the Night King reanimated Dany’s fallen dragon thanks to Bran, and they know Viserion is how the Night King took down The Wall.
If the dragon is powerful enough to blast down a mighty wall that stood for thousands of years, the walls and buildings of Winterfell don’t stand a chance.
Honestly, part of why this theory is so appealing to me is that nobody in any of the strategy sessions mentioned a plan for taking down Viserion.
Surely somebody put some forethought into taking down Viserion.