Bright object limits have been set for the FOC to avoid such damage or residuals. See Section 6.6 of the FOC Instrument Handbook for more details on Detector Overload. When the count reaches 255 the next count will cycle the value for that pixel back to 0 from which it continues counting up.
Saturation is the result of nonlinear behavior which depends on the count rate.
It is possible to have overflow without much saturation or visa versa, or both. It appears I have some overflows in my image. This is usually done in some ad hoc fashion depending on the details of the image. For overflowed stars or compact sources, it can be very difficult, if not impossible, to unambiguously correct the overflows. It appears parts of my image are saturated.