I'm writing in a fantasy setting. My goal is to have noble houses which derived from monarchy but not a monarchy itself.
My idea for what happened is this:
Once upon a time, there was monarchy--there was a king and his subjects were given noble titles and territories. Then, along came a bunch of wizards, who became so powerful that they threatened to overthrow the king. Before they tried, however, the wizards promised the nobles that after the king is no more, the nobles will retain their titles, their lands and pay less taxes. (also, if anyone dared oppose the wizards, they'll have a bad time because the wizards had better weapons than the nobles.) Thus enticed and threatened, most of the nobles chose to do nothing while the capital is seized and the kind overthrown. Ever since, the wizards ran the capital, but the nobles continue to exist as centers of power, even though there will be never be another king who might officiate their titles.
I want to know if this is plausible, specifically, I want to know if it makes sense for the nobles to stand idly by while the wizards overthrew their king. Assuming that it will be costly but not impossible for the nobles to fight the wizards. Would the absence of a king completely invalid the nobles' power, and therefore make the battle to preserve monarchy obligatory for the nobles?