I am starting a Word Bearers force and have it all built and ready to go but i was wondering what kind of tech would they have
I am thinking defilers are ok as the Dark Mech would help them build it and deamons are a go but is there anythig i should not use?

and did Erubus ever die?

Erebus is still alive in the 40th Millenium (read Dark Apostle).

The only thing they would not have, I'm pretty sure, is Defilers - Abaddon had them built for the 13th Black Crusade... You can always just say it's a generic daemon engine though...

I've converted defilers into Myrmidon assault walkers, so you can use the unit entry, but adapt it to be something else. Defilers definitely did not exist, in name, in that era.