Ainge has always been more favorable with players that can play small ball, multiple positions, good hard worker, and can shoot or defend.
Since Mickey cannot do neither at the major level, I don't see a point keeping him. But I followed him in D-League, and I firmly believe his shotblocking, and his mid range/3pt shooting will improve which would lead to him having a good solid rotational back up big position, and possibly even a Serge Ibaka starting type of role.
I actually think Mickey has a great skill set in determining when to jump and when not to. He can have a great future if he can just learn how to improve on overall team defense, like providing weak side help defense, and covering the pick and roll instead of being the last line of defense and going for the block. His shooting also needs to improve since he's so undersized, and definitely needs to bulk up.
Anyways, if we're comparing Mickey to Yabusele, I would take Yabusele's skill set over Mickey's anyday. I can see Yabusele having a fine career, and he's built with a strong frame, and really good quickness for his size.