Rogues feel invincible right now. And they kind of are ;(

So, when this guy is harassing you, travel in ghostwolf form.

When the stunlock starts, immediately start healing your main and have them drop poison cleansing totem.
Once the stunlock ends flame shock rank 1 on the rogue, and back the followers up a bit so he can't run behind them to avoid damage.
Just spam LBs at him, force the cloak and try to keep him in combat or force him to use vanish.

As a warning though, when a rogue dies, 4 new rogues spawn, usually undead or BE (<3 that AOE silence blizz)