I believe Mikey was bumped up to consigliere when Junior took over, at least de facto, though I always thought the problem with Mikey was that he acted more like an enforcer than a consigliere. He was just another yes-man for Junior and never gave any proper advice. A good consigliere is able to advise his boss even if it conflicts with his views, when did Mikey ever blatantly disagree with Junior? Sure he pushed for Tony to get whacked but only after Junior implied he needed to go. Was he a good character? Sure, Al Sapienza is a fantastic mob actor. Was he a good consigliere or a really in-depth character? Ehhhh. Not really, and when it was clear Junior was moving against Tony, the upper administration (Including Mikey and Chucky Signore) had to go, with Junior only being spared because he was related by blood to Tony. So yeah, I'm sure it would've been nice to see Mikey appear for another season or two, I always thought it would've been clever if they kept Jackie Aprile around for the entire first season instead of killing him off so early. Then by Season 2 he dies and we see the power struggle between Junior and Tony, but alas, what happened happened.