Mine didn't. I just checked at KC Elections with their handy "ballot tracker." I mailed my ballot a week ago, from a post office, and it's not there.
So a pleasant elections worker mailed me a link for another ballot that I filled out online (or you can download and fill in at home) that I am taking to a KC dropbox at Magnuson Park. (You can also go downtown to the King Street Station to get a ballot from 10 am to 8 pm.)