If the hexed creature dies before this hex ends, the damage is still dealt. This is especially useful if the target is also hexed with Putrid Bile and/or Icy Veins, creating a rather massive AoE spike upon the target's death. However, keep in mind that Rising Bile will not deal full damage since it ends early.
If this skill is echoed, it can serve as a very powerful timebomb. It can do excesses of 300 damage to foes not equipped with hex removal. Be sure to cast Rising Bile on 2 different targets.
If the same caster renews Rising Bile before it would end, the hex will end at 20 seconds causing no extra damage.