Zaros was quite evidently overconfident in his ability to keep Zamorak secure in the threshold of his mind (no, he did not know the power of the staff, it's power was hidden by a spell (not everything from Ghostly Robes has been disregarded as a misinterpretation of events like Viggora's dialogue), hence the lack of an attempt to talk him down.
As for why he wouldn't just accept the demand or explain things to Zamorak, you have to consider that, up until this point, Zamorak had been Zaros's most trusted general. One of the people he felt confident enough to leave the empire in the hands in just broke that confidence.
Furthermore, Zaros is really self centered. It's not much of a stretch at all to say that he really didn't want to leave the empire under anybody's terms but his own.
01-Dec-2016 03:49:39