From what I understand Monster that normally have higher level than the max level for the TZ (TZ level for normals; TZ level + 2 for champions; and TZ +3 for uniques) keeps his original level and will be exactly the same as his non-terrorized version.
If this is true,
Baal, that has L99, will never be terrorized

(max TZ level is 96...)
And the same will be true for Diablo (L94) if TZ level is 91-
and
Nihlathak (L95) if TZ level is 92-
So, if TZ time is running out, maybe it is better - for XP - to kill more "regular monsters" and let
Baal to be killed after TZ runs out, then rush to kill
Baal 

(or Diablo/
Nihlathak depending on the TZ level...)
fredkid
1137