It is bound to drop off, but not as much as in years past.
With autos, homes, and workplaces well heated, weather plays a lesser role. But, people aren’t doing in winter most of the activities which tends to get them inspired to have ice cream.
They offset the drop by selling ice cream cakes. Birthdays happen year round.

I am not familiar with DQ’s menu.

There is a ice cream shop close to me, that is busy year round. But they also sell hot food items, like burgers, sandwiches, and fried sides. I imagine that they sell more soup and hot stuff, and less ice cream, when it’s cold.

Does anyone know if hot coffee is purchased less in the summer?

I tend to eat more ice cream in the winter than I do during the summer. Once it gets cold enough outside that I have to turn on my heat, my throat begins to feel sore & scratchy. There’s nothing like a good bowl of ice cream to soothe a sore, scratchy throat!!!

The Rita’s Ice stand where I live closes for the winter.

I eat less ice cream in the winter.

In New England several smaller DQ’s close and the owners and family (they work there) go to Florida or the Gulf of Mexico coast to work in the winter.

I can’t speak for the company, of course. But as a consumer, I know that my ice cream consumption goes way down in the winter.

I have never had an ice cream in winter