With reaction wheels it is common to use actuators such as Thrusters and magnetorquers, to account for the saturation of the reaction wheels due to secular/non-cyclic disturbances. However, these disturbances are a result of spacecraft properties such as mass, area, attitude etc. So it is possible under certain conditions that the reaction wheels do not saturate (i.e never reach the maximum angular momentum storage capacity) and can be despun to release the angular momentum that they have build up due to these disturbances. And the torque that is acted on the spacecraft due to deceleration of the wheels (to release the angular momentum) and the changes in attitude and angular velocity (which are the result of the torque) can be counteracted by the typical control manoeuvre of acceleration, coasting and deceleration of the reaction wheels.
What I would like to know if this is a correct understanding or if there is something I have missed out? And also, have there been any missions that have flown with only reaction wheels on board without other actuators for momentum dumping?