I would kill it. Pie bald genetics are inferior and bad for the herd. Its not just a lot of white in the coat, its also a whole lot of other inferior traits. Short legs, short lower jaws, smaller body size, etc.
Sometimes pie bald deer have other poor qualities, but a normal colored coat. The reason I know this is about 7 years ago I shot a doe that had a fully developed lower jaw that was about 4 inches shorter than the top. I researched it and was told it came from the deer having pie bald genetics.