Runes in good hands.

Firstly, the quest is actually bad regardless of the outcome. Usually, we get something useful for completing side quests, but here, the reward is either useless or even harmful.
Secondly, the reward for the mummy quest is the ability to transform into a Necromancer. After summoning Death, you will be able to raise the dead after battle, just like a Necromancer, and you will receive a Necromancer army.
That's all.