Redclanger,
Rotorvating will chop up SOME of the worms for sure but so will digging with a spade for that matter. If you're rotorvating to destroy couch it's better to do this from June until August, hopefully these are dry months and the worms go deep to find moisture
Sprout,
You must rotorvate at least 3 times, after the first time wait for the couch to start showing through again and hit it before it starts storing nutrients in it's roots, and so on another 2 or 3 times. Rotorvating couch just once will make the problem far worse