Wasn't too pleased with the finale either, to be honest.
Apparently, John Wells, the creator of the show, stated that Noel Fisher (Mickey) might not be returning full time next season because of some movie he might be in. He stated that he isn't sure yet and that he needs to check back with him, so I'm guessing they wrote the break-up in their storyline so that Mickey can skip a few episodes if he needs to, just like they did with Carl. It seems that the main reason Carl was sent to juvie is because Ethan Cutkosky who plays him, just started highschool and didn't want to miss his first year, so they wrote him out of the last batch of the episodes which were shot in the fall and coincided with his school schedule.
Anyway, not the strongest finale for what wasn't the strongest season. They dragged the Veronica & Kev storyline for way too long. One bright spot this season was Svetlana who made me laugh the most and I kind of liked Frank being out of the picture a bit. Also the actress playing Bianca is brilliant. They really fleshed out her character tremendously in such a short period.