There is no way City will implode after Guardiola leaves in the way that United have since Ferguson left. The reason is simple. We have a robust structure in place which binds together the owner, the management and the football staff which will not be affected at all by Guardiola leaving. Any new manager will have the full support of that structure, within the same guidelines that Guardiola works under.
Where there may be a drop-off is in on-field performance, depending on the effectiveness of the new manager
Because, let's face it Guardiola is the best. So we may be challengers rather than favourites.
But those worrying about some United-like meltdown should relax a little imo.