Ok sorry. From what I tried and played, they do not switch from any moves that are encored. I've tried using Encore Whimsicott before in Battle Subway, and they so far never switched even when encored into using things like Twave even when Whimsicott has already been paralyzed. It's quite possible that they sometimes do switch.
O yeah, I also noticed that they don't switch anymore even when they have natural cure and are paralyzed (they did back in Gen IV).