He was supposedly tasked with getting into the Champions League. He has achieved that and more so it should be considered a job well done.
However, when a club has very rich owners like City or Chelsea that always makes me consider the manager's job as less secure. That might be unfair but its just the feeling I get.
For one, I get the impression they might be prone to interfering more than other owners. Secondly, buying your way into a CL place is one thing - especially when the other contenders suffer their own dips, as us and Spurs both have to a degree - but the requirement for next season might be a lot more ambitious, and that could be his undoing.
If City's owners want the league or CL next season, and they start deciding for themselves which players they might need for that then Mancini might not be there as long as it might seem now