It’s reduced but not destroyed. According to this, a baked potato still contains 48% of the percent daily value of vitamin C, and even McDonald’s french fries contain 14%.
And… they may not eat vegetables as a straight-up side dish, but if they have a hotdog with 1/2 cup of sauerkraut on it, they’re getting something like 8% of their daily fiber, 17% of their daily vitamin C, and 2 grams of fiber right there, in something they likely consider a condiment.
I’d bet that other vegetable sauces, condiments and garnishes figure in similarly, even if the consumer doesn’t really consider them to be vegetables.