Hey,
Yes. Beniah is interrupted by Two Thousand Horses and remains interrupted until the effect of Two Thousand Horses is completed. Part of the effect of Two Thousand Horses is the effect of the enhancement played with it. The key is that when the enhancement played with it (Death of Unrighteous) completes, Death of Unrighteous is no longer in play (it gets discarded with Rabshakeh) so when Beniah kicks back in and negates characters and enhancements in play it does not affect Death of Unrighteous.
Tschow,
Tim "Sir Nobody" Maly