After watching the latest episode of the Originals I feel like Mikael truly was motivated to kill Klaus because he was a bastard. I mean when they were alone Mikael never even mentioned Esther all he could talk about was destroying Klaus and how they weren't really family even mentioning Klaus's real dad. Yet he never once mentioned Esther in my opinion Mikael was just using Esther as an excuse.
One thing though I am certain of Mikael really is the monster that monsters fear I mean he was in town for a week and he raised hell on a level that I didn't think was possible not to mention his cruelty to his own children.
I mean he's a text book abuser his talk with Rebeckah in VD proves that (he shows remorse then he goes abusive again after a while) to paraphrase Dean Winchester Mikael is the same brand of cockroach as any other abusive parent only bigger the only difference between Mikael and other abusers is the size of his ego.
And with Celeste dead and Klaus rebuilding what he lost I think Mikael will return because Klaus will have more to fight for and I keep getting the feeling that history will repeat itself.