If pickling destroys Vitamin C, how is Sauerkraut rich in Vitamin C?

Vitamin C is destroyed by heat and light. If you use a preservation method that relies on heating the sauerkraut at any stage (hot pickling liquid, water bath or pressure canning the jars) then some vitamin C is destroyed. Exactly how much depends on the process: not all vitamin C is lost immediately so different processes will have different amounts of vitamin C left. And if you use a preservation method that doesn't rely on heat like lacto-fermentation, no vitamin C is lost to heat (some may be lost to light, depending on how you store it).