Hi all, i'm planning on using this when running through Dawnguard, is he and the rieklings essential?

when you fight by side with the Sphere, he is essential and cannot die. Not too sure about the reiklings. Although if you attack the Steadfast Dwarven Sphere and attempt to destroy it yourself, it will die on you. so be careful where you swing.

Ah ok, thank you! I found the Dwarven spider now, trying to solve the rest of the Kagrumez puzzle.

Anytime one of your "pets" that you gather from this dungeon dies, just go back ad get another. They re-spawn.